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PubMedDate not supplied

N-Terminal peptide aldehydes as electrophiles in combinatorial solid phase synthesis of novel peptide isosteres.

N-Terminal peptide aldehydes were synthesized on a solid support and utilized as electrophiles in nucleophilic reactions in order to furnish novel and diverse peptide isosteres. The aldehyde moiety of the peptide was synthesized by coupling a protected aldehyde building block to the peptide and deprotecting it quantitatively in less than 3 min. It was found that protection of the two succeeding amide nitrogens was necessary in order to avoid reaction between the aldehyde and backbone amides. The N-terminal peptide aldehydes were successfully reacted in the following way: (a) reductive amination with a large variety of amines, leading to N-alkyl-gamma-aminobutyric peptide isosteres positioned centrally in the peptide; (b) reductive amination with amino esters, leading to N-terminal 2,5-diketopiperazine peptides; (c) Horner-Wadsworth-Emmons olefination, leading to unsaturated peptide isosteres positioned centrally in the peptide; and (d) Pictet-Spengler condensations, leading to tetrahydro-beta-carbolines either positioned centrally in a peptide or fused with a diketopiperazine ring in the N-terminus of the peptide.

Aldehydes↗
PubMed2002

A general strategy to determine a target DNA sequence of a short peptide: application to a d-peptide.

Short peptides could potentially provide a novel element to read-out DNA sequences from the major groove. However, it is difficult to determine sequence-preference of de novo designed monomeric short peptides. Because DNS-binding affinity and specificity of short peptides are usually much lower than those of native DNA-binding proteins, determining the sequence-preference of short peptides by conventional methods utilized to deduce the target sequence of proteins often produces an unclear outcome. We report here a general strategy to defining the sequence-preference of a DNA-binding short peptide by using the heterodimers. A GCN4 basic region peptide tethers a low-affinity DNA-binding peptide adjacent to a GCN4 binding sequence through the cyclodextrin-adamantane association, thereby increasing local concentration of the low-affinity peptide on degenerated DNA sequences. An increase of the local concentration allows one to select a preferential sequence for the low-affinity DNA binding peptide. The method successfully identified specific sequences of short peptides derived from native DNA-binding proteins. The usefulness of this approach has been demonstrated by identifying preferred DNA targets for a peptide composed only of d-amino acids. The method is potentially applicable not only to artificial peptides, but also to other synthethic ligands.

Amino Acid Sequence↗
PubMedDate not supplied

Mass spectrometric quantitation of peptides and proteins using Stable Isotope Standards and Capture by Anti-Peptide Antibodies (SISCAPA).

A method (denoted SISCAPA) for quantitation of peptides in complex digests is described. In the method, anti-peptide antibodies immobilized on 100 nanoliter nanoaffinity columns are used to enrich specific peptides along with spiked stable-isotope-labeled internal standards of the same sequence. Upon elution from the anti-peptide antibody supports, electrospray mass spectrometry is used to quantitate the peptides (natural and labeled). In a series of pilot experiments, tryptic test peptides were chosen for four proteins of human plasma (hemopexin, alpha1 antichymotrypsin, interleukin-6, and tumor necrosis factor-alpha) from a pool of 10,203 in silico tryptic peptide candidates representing 237 known plasma components. Rabbit polyclonal antibodies raised against the chosen peptide sequences were affinity purified and covalently immobilized on POROS supports. Binding and elution from these supports was shown to provide an average 120-fold enrichment of the antigen peptide relative to others, as measured by selected ion monitoring (SIM) or selected reaction monitoring (SRM) electrospray mass spectrometry. The columns could be recycled with little loss in binding capacity, and generated peptide ion current measurements with cycle-to-cycle coefficients of variation near 5%. Anti-peptide antibody enrichment will contribute to increased sensitivity of MS-based assays, particularly for lower abundance proteins in plasma, and may ultimately allow substitution of a rapid bind/elute process for the time-consuming reverse phase separation now used as a prelude to online MS peptide assays. The method appears suitable for rapid generation of assays for defined proteins, and should find application in the validation of diagnostic protein panels in large sample sets.

Antibodies, Anti-Idiotypic↗
PubMed1995

Comparative effects of atrial natriuretic peptide and brain natriuretic peptide on the aldosterone and pressor responses to angiotensin II in man.

1. Atrial natriuretic peptide and brain natriuretic peptide have similar vasodilator and natriuretic properties, although little information is available regarding their relative effects as antagonists of the renin-angiotensin-aldosterone system. We have therefore compared how atrial natriuretic peptide and brain natriuretic peptide affect the systemic pressor and aldosterone responses to angiotensin II in eight male subjects. 2. Each subject was studied on three separate occasions, when they received a 60-min infusion of placebo, atrial natriuretic peptide (10 pmol min-1 kg-1) or brain natriuretic peptide (10 pmol min-1 kg-1), with a concomitant infusion of angiotensin II (6 ng min-1 kg-1) given for the final 30 min of the infusion period. The change in haemodynamic parameters and plasma aldosterone induced by angiotensin II was measured. Plasma concentrations of atrial natriuretic peptide (182 +/- 23 pmol/l) and brain natriuretic peptide (193 +/- 25 pmol/l) achieved at steady-state during the infusion on each study day were not significantly different. 3. Increases in mean arterial pressure in response to angiotensin II were significantly lowered by concomitant infusion of atrial natriuretic peptide (21.0 +/- 1.7 mmHg) and brain natriuretic peptide (20.1 +/- 1.9 mmHg) compared with placebo (29.0 +/- 4.1 mmHg). There were similar effects on systolic and diastolic blood pressure. Cardiac output was decreased on each study day to the same extent y angiotensin II infusion. Total systemic vascular resistance showed a non-significant trend towards an attenuated response to angiotensin II when atrial natriuretic peptide or brain natriuretic peptide was infused concomitantly in comparison with placebo.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1989

Turnover of Ia-peptide complexes is facilitated in viable antigen-presenting cells: biosynthetic turnover of Ia vs. peptide exchange.

Macrophages and B cells process antigens to produce antigenic peptides that associate with class II major histocompatibility complex molecules (e.g., Ia molecules); these Ia-peptide complexes are recognized by CD4+ T lymphocytes. Processing of the antigen hen egg white lysozyme was inhibited by cycloheximide in peritoneal exudate cells (PECs, largely macrophages), but not in TA3 B-lymphoma cells. The uptake and metabolism of hen egg white lysozyme was largely intact in cycloheximide-treated PECs, implicating a blockade in other steps in the formation of Ia-peptide complexes. Turnover of Ia-peptide complexes was markedly enhanced in viable antigen-presenting cells (TA3 and PEC) as compared to such complexes studied on fixed cells or in isolated preparations of Ia and peptide. In B cells the half-life of Ia-peptide complexes was much shorter than the half-life of the Ia molecules, implying turnover of Ia-peptide complexes by dissociatin and peptide exchange. In PECs, the dissociation of Ia-peptide complexes was more limited; the enhanced Ia-peptide turnover in viable PECs reflected in part biosynthetic turnover of Ia molecules. Specific mechanisms may exist in TA3 cells to facilitate exchange of peptides bound to Ia, allowing recycling of Ia to present another antigenic peptide; such Ia recycling would explain the ability of these cells to process and present antigen in the absence of Ia synthesis.

Animals↗
PubMed1995

Peptide inhibitors of peptidyltransferase alter the conformation of domains IV and V of large subunit rRNA: a model for nascent peptide control of translation.

Peptides of 5 and 8 residues encoded by the leaders of attenuation regulated chloramphenicol-resistance genes inhibit the peptidyltransferase of microorganisms from the three kingdoms. Therefore, the ribosomal target for the peptides is likely to be a conserved structure and/or sequence. The inhibitor peptides "footprint" to nucleotides of domain V in large subunit rRNA when peptide-ribosome complexes are probed with dimethyl sulfate. Accordingly, rRNA was examined as a candidate for the site of peptide binding. Inhibitor peptides MVKTD and MSTSKNAD were mixed with rRNA phenol-extracted from Escherichia coli ribosomes. The conformation of the RNA was then probed by limited digestion with nucleases that cleave at single-stranded (T1 endonuclease) and double-stranded (V1 endonuclease) sites. Both peptides selectively altered the susceptibility of domains IV and V of 23S rRNA to digestion by T1 endonuclease. Peptide effects on cleavage by V1 nuclease were observed only in domain V. The T1 nuclease susceptibility of domain V of in vitro-transcribed 23S rRNA was also altered by the peptides, demonstrating that peptide binding to the rRNA is independent of ribosomal protein. We propose the peptides MVKTD and MSTSKNAD perturb peptidyltransferase center catalytic activities by altering the conformation of domains IV and V of 23S rRNA. These findings provide a general mechanism through which nascent peptides may cis-regulate the catalytic activities of translating ribosomes.

Amino Acid Sequence↗
PubMed1998

A soluble major histocompatibility complex class I peptide-binding platform undergoes a conformational change in response to peptide epitopes.

Class I major histocompatibility complexes (MHC) are heterotrimeric structures comprising heavy chains (HC), beta2-microglobulin (beta2-m), and short antigenic peptides of 8-10 amino acids. These components assemble in the endoplasmic reticulum and are released to the cell surface only when a peptide of the appropriate length and sequence is incorporated into the structure. The binding of beta2-m and peptide to HC is cooperative, and there is indirect evidence that the formation of a stable heterotrimer from an unstable HC:beta2-m heterodimer involves a peptide-induced conformational change in the HC. Such a conformational change could ensure both a strong interaction between the three components and also signal the release of stably assembled class I MHC molecules from the endoplasmic reticulum. A peptide-induced conformational change in HC has been demonstrated in cell lysates lacking beta2-m to which synthetic peptides were added. Many features of this conformational change suggest that it may be physiologically relevant. In an attempt to study the peptide-induced conformational change in detail we have expressed a soluble, truncated form of the mouse H-2Db HC that contains only the peptide binding domains of the class I molecule. We have shown that this peptide-binding "platform" is relatively stable in physiological buffers and undergoes a conformational change that is detectable with antibodies, in response to synthetic peptides. We also show that the structural features of peptides that induce this conformational change in the platform are the same as those required to observe the conformational change in full-length HC. In this respect, therefore, the HC alpha1 and alpha2 domains, which together form the peptide binding site of class I MHC, are able to act independently of the rest of the molecule.

Animals↗
PubMed2000

Structural and functional consequences of peptide-carbohydrate mimicry. Crystal structure of a carbohydrate-mimicking peptide bound to concanavalin A.

The functional consequences of peptide-carbohydrate mimicry were analyzed on the basis of the crystal structure of concanavalin A (ConA) in complex with a carbohydrate-mimicking peptide, DVFYPYPYASGS. The peptide binds to the non-crystallographically related monomers of two independent dimers of ConA in two different modes, in slightly different conformations, demonstrating structural adaptability in ConA-peptide recognition. In one mode, the peptide has maximum interactions with ConA, and in the other, it shows relatively fewer contacts within this site but significant contacts with the symmetry-related subunit. Neither of the peptide binding sites overlaps with the structurally characterized mannose and trimannose binding sites on ConA. Despite this, the functional mimicry between the peptide and carbohydrate ligands was evident. The peptide-inhibited ConA induced T cell proliferation in a dose-dependent manner. The effect of the designed analogs of the peptide on ConA-induced T cell proliferation and their recognition by the antibody response against alpha-d-mannopyranoside indicate a role for aromatic residues in functional mimicry. Although the functional mimicry was observed between the peptide and carbohydrate moieties, the crystal structure of the ConA-peptide complex revealed that the two peptide binding sites are independent of the methyl alpha-d-mannopyranoside binding site.

Binding Sites↗
PubMed1997

The critical role of a solvent-exposed residue of an MHC class I-restricted peptide in MHC-peptide binding.

The immunodominant ovalbumin257-264 (OVA-8, SIINFEKL) and herpes simplex virus gB496-503 (HSV-8, SSIEFARL) peptides share 50% amino acid identity (residues P1, P3, P5 and P8) and bind with comparable efficacy to the murine MHC-encoded class I molecule H-2Kb. However, these two peptides bind differently to H-2Kbm8, a natural H-2Kb variant with a substitution in four amino acids on the floor of the peptide-binding site; HSV-8 binds with high and OVA-8 with a relatively low efficacy. To investigate which of the non-homologous peptide residues were responsible for this differential binding, we used substituted peptide variants and the class I thermodynamic stabilization assay. Variation at the solvent-exposed peptide residues P6 and P7 did not appreciably influence binding. By contrast, variation at the buried P2 and, surprisingly, at the solvent-exposed P4 residue was found to be important. Transplantation of the HSV-8 P2 or P4 residues onto the OVA-8 backbone created variant peptides O2S (P2I-->S) and O4E (P4N-->E) that bound considerably better to H-2Kbm8 than OVA-8. Furthermore, the double-substituted peptide, O2S4E, bound even better, revealing a cooperative effect of the two residues. The reciprocally substituted peptides H2I and H4N, generated by grafting the OVA-8 P2 and P4 residues onto the HSV-8 backbone respectively, bound to H-2Kbm8 slightly worse than HSV-8 but the double-substituted peptide H2I4N bound as poorly as OVA-8. Effects exerted by the P4 residue, which is solvent accessible and therefore available for the TCR contact, demonstrated that exposed peptide residues can, in certain situations, influence not only the TCR contact but also MHC-peptide binding.

Animals↗
PubMed2004

Cardioprotective functions of atrial natriuretic peptide and B-type natriuretic peptide: a brief review.

1. If one was to design a hormone to protect the heart, it would have a number of features shown by the cardiac natriuretic peptides atrial natriuretic peptide (ANP) and B-type natriuretic peptide (BNP). These hormones are made in cardiomyocytes and are released into the circulation in response to atrial and ventricular stretch, respectively. Atrial natriuretic peptide and BNP can reduce the preload and after-load in normal and failing hearts. They reduce blood volume over the short term by sequestering plasma and over the longer term by promoting renal salt and water excretion and by antagonizing the renin-angiotensin-aldosterone system at many levels. Each of these actions affords indirect benefit to a volume- or pressure-threatened heart. 2. Recent studies have identified additional modes of action of the natriuretic peptides that may also confer cardioprotective benefits, especially in heart disease. The emerging findings are: (i) that ANP and BNP antagonize the cardiac hypertrophic action of angiotensin II and continue working under conditions where endothelial nitric oxide (NO) function is compromised, such as in the presence of high glucose in diabetes; (ii) they potentiate the bradycardia caused by inhibitory ('autoprotective') cardio-cardiac reflexes; and, furthermore, (iii) BNP can suppress cardiac sympathetic nerve activity in humans, including those with heart failure. Thus, it appears that natriuretic peptides can shift sympathovagal balance in a beneficial direction (away from the sympathetic). The vagal reflex and antihypertrophic actions of the peptides are mediated by particulate guanylyl cyclase (pGC) natriuretic peptide receptors. 3. The multiple synergistic actions of the natriuretic peptides make them and their pGC receptors attractive targets for therapy in heart disease. Encouragingly, exogenous natriuretic peptides remain effective even when endogenous peptide levels are raised, as is the case in heart failure. They also remain effective in disease states where other protective mechanisms, such as the NO system, have become ineffective, offering yet further encouragement for the therapeutic use of the natriuretic peptides.

Animals↗
PubMed2004

Regulation of fungal infection by a combination of amphotericin B and peptide 2, a lactoferrin peptide that activates neutrophils.

To establish a novel strategy for the control of fungal infection, we examined the antifungal and neutrophil-activating activities of antimicrobial peptides. The duration of survival of 50% of mice injected with a lethal dose of Candida albicans (5 x 10(8) cells) or Aspergillus fumigatus (1 x 10(8) cells) was prolonged 3 to 5 days by the injection of 10 microg of peptide 2 (a lactoferrin peptide) and 10 microg of alpha-defensin 1 for five consecutive days and was prolonged 5 to 13 days by the injection of 0.1 microg of granulocyte-monocyte colony-stimulating factor (GM-CSF) and 0.5 microg of amphotericin B. When mice received a combined injection of peptide 2 (10 microg/day) with amphotericin B (0.5 microg/day) for 5 days after the lethal fungal inoculation, their survival was greatly prolonged and some mice continued to live for more than 5 weeks, although the effective doses of peptide 2 for 50 and 100% suppression of Candida or Aspergillus colony formation were about one-third and one-half those of amphotericin B, respectively. In vitro, peptide 2 as well as GM-CSF increased the Candida and Aspergillus killing activities of neutrophils, but peptides such as alpha-defensin 1, beta-defensin 2, and histatin 5 did not upregulate the killing activity. GM-CSF together with peptide 2 but not other peptides enhanced the production of superoxide (O2-) by neutrophils. The upregulation by peptide 2 was confirmed by the activation of the O2- -generating pathway, i.e., activation of large-molecule guanine binding protein, phosphatidyl-inositol 3-kinase, protein kinase C, and p47phox as well as p67phox. In conclusion, different from natural antimicrobial peptides, peptide 2 has a potent neutrophil-activating effect which could be advantageous for its clinical use in combination with antifungal drugs.

Amphotericin B↗
PubMed1992

Human C-type natriuretic peptide. Characterization of the gene and peptide.

We isolated the human C-type natriuretic peptide gene and identified the peptide in the brain. The human C-type natriuretic peptide gene appeared to be composed of at least two exons and one intron. In the 5'-flanking region, there is an array of cis elements (an inverted CCAAT box, two GC boxes, and a cyclic AMP response element-like sequence) that is not present in upstream sequences of the atrial and brain natriuretic peptide genes. Analysis of the deduced amino acid sequence revealed that human prepro C-type natriuretic peptide comprises 126 amino acids and that the C-terminal 22-residue peptide (G-L-S-K-G-C-F-G-L-K-L-D-R-I-G-S-M-S-G-L-G-C) preceded by Lys-Lys is identical to the porcine counterpart. However, replacement of two amino acids took place in the C-terminal 53-residue sequence, corresponding to another endogenous form of the peptide. Reverse-phase high-performance liquid chromatography coupled with a radioimmunoassay for C-type natriuretic peptide demonstrated that it occurs in the human brain. C-type natriuretic peptide-like immunoreactivity was detected in discrete regions of the human brain, and its level was 10-fold higher than the atrial and brain natriuretic peptide levels, raising the possibility that C-type natriuretic peptide is the major natriuretic peptide in the human brain.

Amino Acid Sequence↗
PubMed2002

Modification of a tumor-derived peptide at an HLA-A2 anchor residue can alter the conformation of the MHC-peptide complex: probing with TCR-like recombinant antibodies.

A common assumption about peptide binding to the class I MHC complex is that each residue in the peptide binds independently. Based on this assumption, modifications in class I MHC anchor positions were used to improve the binding properties of low-affinity peptides (termed altered peptide ligands), especially in the case when tumor-associated peptides are used for immunotherapy. Using a new molecular tool in the form of recombinant Abs endowed with Ag-specific MHC-restricted specificity of T cells, we show that changes in the identity of anchor residues may have significant effects, such as altering the conformation of the peptide-MHC complex, and as a consequence, may affect the TCR-contacting residues. We herein demonstrate that the binding of TCR-like recombinant Abs, specific for the melanoma differentiation Ag gp100 T cell epitope G9-209, is entirely dependent on the identity of a single peptide anchor residue at position 2. An example is shown in which TCR-like Abs can recognize the specific complex only when a modified peptide, G9-209-2 M, with improved affinity to HLA-A2 was used, but not with the unmodified natural peptide. Importantly, these results demonstrate, using a novel molecular tool, that modifications at anchor residues can dramatically influence the conformation of the MHC peptide groove and thus may have a profound effect on TCR interactions. Moreover, these results may have important implications in designing modifications in peptides for cancer immunotherapy, because most such peptides studied are of low affinity.

Amino Acid Substitution↗
PubMed1995

Reversal of acute experimental autoimmune encephalomyelitis and prevention of relapses by treatment with a myelin basic protein peptide analogue modified to form long-lived peptide-MHC complexes.

Experimental autoimmune encephalomyelitis (EAE) is an autoimmune disease induced by immunization with myelin basic protein (MBP), proteolipid protein, or encephalitogenic peptides from these myelin components. EAE resembles basic protein multiple sclerosis in some of its clinical and histologic features, and serves as an experimental model for this and other autoimmune diseases. In this study, we examine i.v. peptide therapy of EAE in detail, and show that repeated i.v. injections of MBP peptides effectively treat EAE in (PLJxSJL)F1 mice. In this study, administration of the immunodominant epitope (MBP Ac1-11) prevents MBP-induced disease, whereas the subdominant epitope MBP 31-47 is neither required nor sufficient. Intravenous administration of substituted MBP peptide analogues is also effective in treating EAE, provided the peptide side chains presumed to be involved in TCR contact and MHC binding are preserved. A substituted MBP peptide analogue that forms long-lived peptide-MHC complexes in vivo is more effective than the unmodified MBP peptide. Lower doses of the substituted peptide analogue are effective, and the effect is longer lasting than treatment with the unmodified peptide. Clinical signs of EAE are reversed by injection of the substituted peptide during the acute phase of disease. Moreover, treatment of mice in the remission phase of EAE results in a dramatically reduced incidence of relapse. In summary, we have shown that EAE can be reversed after onset and treated during remission with an MBP peptide analogue that has been modified for improved therapeutic potency.

Amino Acid Sequence↗
PubMed1993

Direct detection of major histocompatibility complex class I binding to antigenic peptides using surface plasmon resonance. Peptide immobilization and characterization of binding specificity.

We have developed model systems in which the binding of purified, genetically engineered, soluble analogues of major histocompatibility complex (MHC) class I molecules to immobilized antigenic peptides can be monitored in real time using surface plasmon resonance (SPR). Synthetic analogues of several peptides known to bind different mouse and human MHC class I molecules were prepared with cysteine residues substituted at appropriate positions. The analogue peptides were immobilized via the bifunctional reagent N-gamma-maleimidobutyryloxy-succinimide to amino groups generated on the dextran-modified gold surface of a biosensor flow cell. Using this approach, each position in the sequence of an H-2Ld-specific viral peptide, pMCMV (YPHFMPTNL), was used for coupling, and the resulting surfaces were tested for binding of the soluble analogue of H-2Ld, H-2Lds. In accord with our previously described H-2Ld/pMCMV three-dimensional structural model, only those residues of the peptide that remain exposed following binding (positions 4-8) can be replaced by cysteine and used for coupling. Stable binding of soluble MHC class I molecules, H-2Lds, H-2Dds, H-2Kbs, and HLA-A2s to their respective immobilized cognate peptides was detected by SPR. Specificity of the peptide/MHC interaction was characterized both by direct binding using immobilized peptides and by competition with peptides in solution, and in general was consistent with known immunological reactivity. Some peptides bound not only their cognate MHC molecule, but others at lower apparent affinity. Measurement of real time binding of MHC class I molecules to peptides immobilized through specific side chains suggests the application of a similar approach to the study of the interaction of peptides with a wide variety of peptide-binding macromolecules.

Alleles↗
PubMed1996

Identification of elements of the peptide binding site of DnaK by peptide cross-linking.

We used photocross-linking of peptides to DnaK to identify elements of the peptide binding site of DnaK. We attached a photoactivatable group (N-hydroxysuccinimidyl-4-azido-salicylic acid (NHS-ASA) or N-iodoacetamidobutyl-4-azido-salicylic acid (I-ABASA)) to different positions on peptide C of the vesicular stomatitis virus glycoprotein, 125I-radiolabeled the cross-linker, cross-linked the peptide to DnaK by UV irradiation, and then determined the amino acid residues of DnaK that were cross-linked to the peptide. Limited trypsin digestion of the DnaK-peptide complex revealed that the derivatives modified with photoactivatable cross-linker peptide C cross-linked to a C-terminal fragment of DnaK and that the N-terminal 45-kDa fragment of DnaK was not cross-linked by these modified peptides. The attachment points of the three peptide C derivatives carrying photoactivatable cross-linkers at different locations on the peptide, PepC-ASA, PepC-S7C-ABASA, and PepC-S8C-ABASA, have been identified as Arg-536, Arg-527, and His-541 of DnaK, respectively. Thus all three peptides cross-linked to amino acids located close together in a sequence that includes one end of the long alpha-helix in the NMR-based secondary structure model of the peptide binding domain of Hsp70 family (Morshauser, R., Wang, H., Flynn, G., and Zuiderweg, E. (1995) Biochemistry 34, 6261-6266).

Amino Acid Sequence↗
PubMed1996

Inhibition of human complement by a C3-binding peptide isolated from a phage-displayed random peptide library.

We have screened a phage-displayed random peptide library for binding to C3b, the proteolytically activated form of complement component C3, and have identified a novel peptide that suppresses complement activation. This phage-displayed peptide bound to C3, C3b, and C3c, but not to C3d, indicating that it binds to the C3c region of C3. A synthetic 27-amino acid peptide corresponding to the phage-displayed peptide also bound to C3 and C3 fragments and inhibited both the classical and alternative pathways of complement activation. The inhibition of complement activation was reversible. Studies with overlapping peptides indicated that the functional activity was located in the cyclic 13-amino acid N-terminal region (ICVVQDWGHHRCT) of the parent peptide. Reduction and alkylation of this 13-residue synthetic peptide destroyed its inhibitory activity. Analysis of the mechanism of inhibition revealed that the peptide inhibited C3 cleavage in normal human serum as well as when the alternative pathway was reconstituted with purified complement components, and the observed inhibition was not due to sterically hindered access to the C3a/C3b cleavage site. Further, the peptide did not inhibit the cleavage of factor B, indicating that it did not affect the interaction of CA with factor B or the formation of C3b,Bb. The peptide also had no effect on the binding of properdin to C3, demonstrating that the observed inhibition of C3 cleavage in normal human serum was not due in part to its effect on the properdin-stabilized C3 convertase, C3b,Bb,P. These results indicate that the peptide we have identified interacts with C3 to inhibit its activation.

Amino Acid Sequence↗
PubMed1995

Regulation of glucagon-like peptide-1-(7-36) amide, peptide YY, and neurotensin secretion by neurotransmitters and gut hormones in the isolated vascularly perfused rat ileum.

Neurotensin (NT), peptide YY (PYY), and several peptides derived from proglucagon are promptly released from endocrine cells of the distal part of the gut after oral ingestion of a meal, thus suggesting that release of these peptides is partly under neural and/or hormonal control. Our previous studies conducted with a model of isolated vascularly perfused rat colon showed that colonic L cells are highly responsive to several transmitters of the gut and to the hormonal peptide GIP. To test the possibility that hormones produced by the proximal small intestine or transmitters of the enteric nervous system may also modulate the secretory activity of the ileal L cells, various intestinal regulatory peptides and neurotransmitters were administered intraarterially for 30 min in the isolated vascularly perfused rat ileum preparation. The secretory activity of the ileal N cells was comparatively assessed. The release of NT, PYY, and glucagon-like peptide-1 (GLP-1) in the portal effluent was measured with specific RIAs. The muscarinic cholinergic agonist bethanechol at a concentration of 10(-4) M provoked a biphasic release of PYY, GLP-1, and NT, consisting of an early peak followed by a sustained response. Similarly, bombesin (10(-7) M) induced a marked biphasic release of PYY and GLP-1. In contrast, the NT response was essentially monophasic, characterized by an early peak secretion. Tetrodotoxin did not modify the bombesin-induced release of PYY, GLP-1, and NT. The beta-adrenergic agonist isoproterenol at a concentration of 10(-6) M induced a transient rise in portal PYY and GLP-1 concentrations, whereas the effect on NT release was clearly biphasic. Calcitonin gene-related peptide (5 x 10(-8) M) induced a dramatic rise in PYY, GLP-1, and NT immunoreactivities in the portal effluent (peaks at 600%, 500%, and 550% of the basal values, respectively, 4 mi n after the start of infusion). Intraarterial infusion of GIP over the concentration range (0.5-3 nM) evoked a significant increase in portal concentration of the three peptides only at the threshold concentration of 3 nM. Secretin (50 pM) or cholecystokinin (50 pM) did not affect the release of ileal hormones. In conclusion, ileal L and N cells respond to a variety of transmitters of the gut. The pattern of peptide release depends on the cell type studied. The two cosynthesized peptides, PYY and GLP-1, appear to be cosecreted in the conditions of the present study.

Animals↗