Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “PEPTIDES”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 829 records · Page 46Linked to original sources
PubMed1993

Early detection of IgA specific antibodies in HIV-1 infected children by peptide-ELISA and peptide time-resolved fluoro-immunoassay.

The presence of specific IgA antibodies in sera from 25 infants born to HIV-1 seropositive mothers was investigated by peptide-ELISA and peptide time-resolved fluoro-immunoassay (TR-FIA). The infants had been monitored at different times after birth for clinical signs and/or symptoms of HIV-1 infection and for detection of HIV-1 in lymphocyte cultures. Serum samples had also been tested for HIV-1 IgG antibodies by commercial ELISA and Western blot and for p24 antigen. Eleven of 25 children were then identified as infected. IgA detection was performed after rProtein G treatment to remove interfering IgG. In the infected group, IgA specific antibodies to a synthetic peptide representing a highly conserved region of the transmembrane glycoprotein gp41 (env: 594-613) were detected in 27 (73%) out of 37 serum samples (9 of 11 children) by the peptide-ELISA test. IgA specific antibodies to the same peptide were found in 30 (81%) sera (9 of 11 children) by the peptide-TR-FIA. Specific HIV-1 IgA antibodies were detected as early as 2 months of age in serum samples from five out of seven children (71% sensitivity) using peptide-ELISA and from six out of seven (86% sensitivity) by peptide-TR-FIA. Conversely, IgA specific antibodies to HIV-1 were absent in two infected children as well as in the sera of all uninfected children tested during the follow up period. Since maternal IgA does not cross the placenta, IgA detection in the serum of the infant is indicative of HIV-1 infection.(ABSTRACT TRUNCATED AT 250 WORDS)

Enzyme-Linked Immunosorbent Assay↗
PubMed2001

HLA-DR53 molecules restrict glutamic acid decarboxylase peptide presentation to T cells of a Type I diabetes patient: specification of the trimolecular HLA-peptide/T-cell receptor complex.

AIMS/HYPOTHESIS: Our aim was to define the molecular specificity of glutamic acid decarboxylase-specific T-cells isolated from a patient (patient 40) with recent onset Type I (insulin-depent) diabetes mellitus. METHODS: The peptide epitope was defined using synthetic peptides to identify the minimal sequence required for T-cell activation and to determine the amino acids that contribute either to MHC binding or T-cell receptor signaling. The MHC class II-restricted peptide presentation was determined using a panel of allogeneic antigen-presenting cells and murine fibroblast-cell lines transfected to express individual human class II alleles and by blocking studies with monoclonal antibodies. The T-cell receptor was also molecularly characterized. RESULTS: Despite that patient 40 carries high-risk alleles of the DRB1 and DQB1 loci, his T-cells recognize a glutamic acid decarboxylase-derived peptide in association with class II, DR53, molecules. Although anchor residues for DR53 molecules have not yet been determined, it was possible to model epitope binding based on sequence comparisons with other class II molecules associated with susceptibility or protection for Type I diabetes. CONCLUSION/INTERPRETATION: The complete molecular specification of the MHC-peptide ligand and the T-cell receptor complex of glutamic acid decarboxylase-specific T-cells will enable analysis of strategies designed to alter T-cell function. For example, the role of altered peptide ligands or T-cell receptor-specific peptides can be studied using a model whose components reflect the natural affinities of MHC-peptide and T-cell receptor-ligand interactions selected in response to this important autoantigen.

Amino Acid Sequence↗
PubMed1998

Crucial role of N-terminal residue of binding peptides in recognition of the monoclonal antibody specific for the peptide-HLA-B5, -B35 complex.

The monoclonal antibody (mAb) 4D12 specific for the HLA-B5, -B35 cross-reacting group (CREG) bound to a fraction of HLA-B*3501 and HLA-B*5101 molecules carrying self-peptides. Analysis of the binding of mAb 4D12 to HLA-B*3501 and -B*5101 molecules pulsed with chemically synthesized peptides revealed that this mAb recognizes a restricted number of peptides and that P1 of the bound peptides critically influences its binding. The 4D12 mAb bound only to HLA-B*3501 molecules carrying peptides with Asn, Asp, Glu, Ser, and Val at P1. Analysis using an HLA-B*3501 crystallographic model suggested that 4D12 may recognize the side chain of the P1 residue that is pointing to the solvent. On the other hand, 4D12 bound only to HLA-B*5101 molecules carrying peptides with Asn or Asp at P1, suggesting that the 4D12 epitope formed by Glu, Ser, or Val at P1 and the A-pocket was changed by the substitution of His for Tyr at residue 171 of HLA-B*3501 molecules. This was confirmed by testing the binding of mAb 4D12 to HLA-B*3501 mutant molecules at residue 171 carrying these peptides. These results together suggest that the conformation of the A-pocket and its hydrogen bound network with the P1 residue is also critical for the binding of mAb 4D12. The present study shows the molecular basis of the specificity of 4D12 for the peptide-HLA class I complex.

Amino Acid Sequence↗
PubMed1991

Inhibition of bovine brain calmodulin-dependent cGMP phosphodiesterase by peptide and non-peptide angiotensin receptor ligands.

Inhibition of a purified 60 KDa bovine brain calmodulin-dependent cGMP phosphodiesterase (PDE) was investigated for a number of peptides and non-peptides which are known to bind to angiotensin (ANG) receptors. The peptide antagonists sarilesin and sarmesin had KI = 120 and greater than 200 microM respectively, and the peptide agonists ANG II and ANG III had KI = greater than 200 and 45 microM respectively. Non-peptide ANG receptor antagonists related to DuP 753 exhibited KI values in the same range. For both peptide and non-peptide antagonists, inhibitory activities in the PDE assay reflected the order of antagonist potencies at ANG receptors in the rat isolated uterus assay and binding affinities at ANG receptors in rat uterine membranes, suggesting that molecular recognition factors are similar for both ANG receptors and cGMP PDE. The vasodilatory and blood pressure lowering effects of compounds related to DuP 753 may be due in part to inhibition of cGMP PDE. The differential effects of ANG II and ANG III at target tissues may relate in part to the marked differences in cGMP PDE inhibition associated with these two peptides hormones.

1-Sarcosine-8-Isoleucine Angiotensin II↗
PubMed1996

The TRH-like peptides in rabbit testis are different from the TRH-like peptide in the prostate.

Human seminal fluid contains a number of tripeptide amides with similar structures to thyrotropin releasing hormone (TRH), two of which have been identified as pGlu-Glu-Pro amide and pGlu-Phe-Pro amide. To determine whether these peptides originate in the same tissues and have the same molecular origin, TRH-immunoreactive peptides were extracted from the prostate and testis of the rabbit, purified by ion exchange chromatography and HPLC, and identified by co-chromatography with 3H-labelled marker peptides. In addition, trypsin digestion was used to release TRH-like tripeptides from N-extended forms of these peptides. The sole TRH-like peptide in the prostate was shown to be pGlu-Glu-Pro amide; it was not accompanied by a detectable amount of pGlu-Phe-Pro amide. The prostate also appeared to contain a very small amount of N-extended forms of these peptides. In contrast to the prostate, the testis contained high concentrations of N-extended forms of pGlu-Phe-Pro amide but essentially no tripeptide. The testis also contained N-extended forms of two other neutral TRH-like peptides which were less hydrophobic than pGlu-Phe-Pro amide. Neither the prostate nor the testis contained a significant amount of TRH. The results show that in the rabbit the TRH-like peptides pGlu-Glu-Pro amide and pGlu-Phe-Pro amide occur in different tissues and appear to be formed from different precursors.

Amino Acid Sequence↗
PubMed1992

HS-142-1, a novel non-peptide ANP antagonist, blocks the cyclic GMP production elicited by natriuretic peptides in PC12 and NG108-15 cells.

HS-142-1 is a novel non-peptide antagonist for atrial natriuretic peptide (ANP) receptor. The effect of HS-142-1 on the cyclic GMP production elicited by natriuretic peptides in neuronal cell lines, PC12 and NG108-15 was examined. Natriuretic peptides such as ANP, brain natriuretic peptide (BNP), and C-type natriuretic peptide (CNP) enhanced cyclic GMP production in a dose-dependent manner. HS-142-1 inhibited cyclic GMP accumulation elicited by natriuretic peptides in a dose-dependent fashion in both cells. The results suggest that HS-142-1 will be an important tool for identification and understanding of the mechanisms by which natriuretic peptides act in nervous systems.

Animals↗
PubMed1992

Pituitary adenylate cyclase activating peptide: a novel vasoactive intestinal peptide-like neuropeptide in the gut.

Pituitary adenylate cyclase activating peptide (PACAP) is a vasoactive intestinal peptide (VIP)-like hypothalamic peptide occurring in two forms, PACAP-27 and the C-terminally extended PACAP-38. The predicted rat and human PACAP sequence is identical to the isolated ovine one. In the present study, the occurrence and distribution of PACAP-like peptides were examined in the gut of several species by immunocytochemistry and immunochemistry using an antibody raised against PACAP-27. PACAP-like immunoreactivity was observed in nerve fibers in the gut wall of all species examined (chicken, mouse, rat, hamster, guinea-pig, ferret, cat, pig, sheep and man). In the chicken and human gut, immunoreactive fibers were numerous in all layers. In the other species examined the fibers were predominantly found in the myenteric ganglia and smooth muscle. Delicate PACAP-immunoreactive fibers were seen in the gastric mucosa of mouse, rat, hamster and man but not in the other species examined. The chicken proventriculus harbored numerous PACAP-immunoreactive endocrine cells which were identical with the serotonin-containing cells storing gastrin-releasing peptide. PACAP-immunoreactive nerve cell bodies were numerous in the submucous ganglia and moderate in number in the myenteric ganglia of the human gut. They were few in the intramural ganglia of the other species examined. Extrinsic denervation (performed on segments of rat and guinea-pig small intestine) did not visibly affect the PACAP innervation, indicating an intramural origin of most PACAP-immunoreactive fibers. Double immunostaining for VIP and PACAP revealed co-existence of the two peptides in nerve cell bodies and nerve fibers of the human and chicken gut and in fibers in the gastric mucosa of mouse and rat. In all other species examined and in all other locations in the gut PACAP-immunoreactive nerve cell bodies and nerve fibers were distinct from those storing VIP; many of them contained gastrin-releasing peptide instead. Immunochemistry revealed PACAP-like peptides in gut extracts of all species studied; upon high performance liquid chromatography the immunoreactive material co-eluted with synthetic PACAP-27. The distribution of PACAP-immunoreactive nerve cell bodies and nerve fibers in the gut wall suggests their involvement in the regulation of both motor and secretory activities.

Amino Acid Sequence↗
PubMed2002

Roles of peptide-peptide charge interaction and lipid phase separation in helix-helix association in lipid bilayer.

The roles of peptide-peptide charged interaction and lipid phase separation in helix-helix association in lipid bilayers were investigated using a model peptide, P(24), as a transmembrane alpha-helical peptide, and its four analogues. Fluorescence amino acids, tryptophan (P(24)W) and pyrenylalanine (P(24)Pya), were introduced into the sequence of P(24), respectively. Association of these peptides permits the resonance excitation energy transfer between tryptophan in P(24)W and pyrenylalanine in P(24)Pya or excimer formation between P(24)Pya themselves. To evaluate the effect of charged interaction on the association between alpha-helical transmembrane segments in membrane proteins, charged amino acids, glutamic acid (P(24)EW) and lysine (P(24)KPya), were introduced into P(24)W and P(24)Pya, respectively. Energy transfer experiments indicated that the charged interaction between the positive charge of lysine residue in P(24)KPya and the negative charge of glutamic acid residue in P(24)EW did not affect the aggregation of transmembrane peptides in lipid membranes. As the content ratio of sphingomyelin (SM) and cholesterol (Ch) was increased in the egg phosphatidylcholine (PC), the stronger excimer fluorescence spectra of P(24)Pya were observed, indicating that the co-existence of SM and Ch in PC liposomes, that is, the raft of SM and Ch, promotes the aggregation of the alpha-helical transmembrane peptides in lipid bilayers. Since the increase in the contents of SM and Ch leads to the decrease in the content of liquid crystalline-order phase, the moving area of transmembrane peptides might be limited in the liposomes, resulting in easy formation of the excimer in the presence of the lipid-raft.

Amino Acid Sequence↗
PubMed1991

Dynamics and aggregation of the peptide ion channel alamethicin. Measurements using spin-labeled peptides.

Two spin-labeled derivatives of the ion conductive peptide alamethicin were synthesized and used to examine its binding and state of aggregation. One derivative was spin labeled at the C-terminus and the other, a leucine analogue, was spin labeled at the N-terminus. In methanol, both the C and N terminal labeled peptides were monomeric. In aqueous solution, the C-terminal derivative was monomeric at low concentrations, but aggregated at higher concentrations with a critical concentration of 23 microM. In the membrane, the C-terminal label was localized to the membrane-aqueous interface using 13C-NMR, and could assume more than one orientation. The membrane binding of the C-terminal derivative was examined using EPR, and it exhibited a cooperativity seen previously for native alamethicin. However, this cooperativity was not the result of an aggregation of the peptide in the membrane. When the spectra of either the C or N-terminal labeled peptide were examined over a wide range of membrane lipid to peptide ratios, no evidence for aggregation could be found and the peptides remained monomeric under all conditions examined. Because electrical measurements on this peptide provide strong evidence for an ion-conductive aggregate, the ion-conductive form of alamethicin likely represents a minor fraction of the total membrane bound peptide.

Alamethicin↗
PubMed2003

Crystal structure of MHC class II I-Ab in complex with a human CLIP peptide: prediction of an I-Ab peptide-binding motif.

Association between the class II major histocompatibility complex (MHC) and the class II invariant chain-associated peptide (CLIP) occurs naturally as an intermediate step in the MHC class II processing pathway. Here, we report the crystal structure of the murine class II MHC molecule I-A(b) in complex with human CLIP at 2.15A resolution. The structure of I-A(b) accounts, via the peptide-binding groove's unique physicochemistry, for the distinct peptide repertoire bound by this allele. CLIP adopts a similar conformation to peptides bound by other I-A alleles, reinforcing the notion that CLIP is presented as a conventional peptide antigen. When compared to the related HLA-DR3/CLIP complex structure, the CLIP peptide displays a slightly different conformation and distinct interaction pattern with residues in I-A(b). In addition, after examining the published sequences of peptides presented by I-A(b), we discuss the possibility of predicting peptide alignment in the I-A(b) binding groove using a simple scoring matrix.

Amino Acid Sequence↗
PubMed1996

A proenkephalin A-derived peptide analogous to bovine adrenal peptide E from frog brain: purification, synthesis, and behavioral effects.

A peptide derived from the posttranslational processing of proenkephalin A was isolated from an extract of the brain of the European green frog Rana ridibunda and its primary structure established as: Tyr-Gly-Gly-Phe-Met-Arg-Arg-Val-Gly-Arg10- Pro-Glu-Trp-Trp-Gln-Asp-Tyr-Gln-Lys-Arg20-Tyr-Gly-Gly-Phe-Met. The structure was confirmed by chemical synthesis. The peptide represents an amphibian equivalent of bovine adrenal peptide E [preproenkephalin A (206-230)-peptide] but the sequence contains two amino acid substitutions (Met15-->Gln and Leu25-->Met) compared with the mammalian peptide. The data support previous hypotheses that the Leu-enkephalin sequence is not present in preproenkephalin A of amphibians. Intracerebroventricular injections of frog peptide E (10 and 100 ng) in mice had no significant effect on horizontal locomotor activity. The peptide, in doses up to 1 microgram, had no effect on latency of escape jumping in the hot plate test and the peptide (100 ng) did not modify responses (paw licking, rearing, and escape jumping) in morphine-treated mice.

Adrenal Glands↗
PubMed1998

A hydrophobic peptide (VAP-peptide) of the silkworm, Bombyx mori: a unique role for adult activity proposed from gene expression and production at the terminal phase of metamorphosis.

A unique hydrophobic peptide (VAP-peptide) isolated from male adult heads of the silkworm, Bombyx mori, has been shown to act as a synergist to the diapause hormone when administered exogenously. Here, we investigated the true role of the endogenous VAP-peptide on differentiation and development of adult organs in the silkworm. By northern blot analyses, the VAP-peptide gene was shown to be exclusively expressed at the terminal phase of adult development in epithelial tissues, especially in the wing and the thoracic integument. In situ hybridization analysis revealed that the gene was highly expressed in the epidermal cells of the wing vein and the thoracic integument. The stage- and tissue-dependent gene expression were clearly correlated to the accumulation profile of VAP-peptide. In the adult thoracic integument, VAP-peptide was predominantly deposited in the cuticle layer. Affinity chromatography indicated the ability of VAP-peptide to bind to chitin. Based on its expression patterns, localization, and chemical properties, VAP-peptide is conceived to be a structural protein that participates in mechanical strengthening of specific cuticle structures, supporting their physical requirements in the adult life of the silkworm.

Animals↗
PubMed1998

Direct mass spectrometric peptide profiling and sequencing of single neurons reveals differential peptide patterns in a small neuronal network.

Mass spectrometry (MS) was employed to detect and structurally characterize peptides in two functionally related neurons, named VD1 and RPD2, which form a network involved in the modulation of heartbeat in Lymnaea. Matrix-assisted laser desorption/ionization MS, directly applied to single neurons VD1 and RPD2, showed overlapping yet distinct mass profiles, with a subset of putative peptides specifically present in neuron VD1. Direct tandem MS of a single VD1 neuron revealed the primary structures of the VD1-specific peptides, which were identified as members of the family of small cardioactive peptides. Based on the tandem MS data, a degenerate oligonucleotide was made for use in a polymerase chain reaction strategy to isolate the cDNA encoding the precursor to the small cardioactive peptides from a brain-specific cDNA library. The calculated masses of the mature, posttranslationally modified peptides, as predicted from the corresponding cDNA, agreed with the measured masses of the actual peptides, as detected in single-cell MS analysis. In situ hybridization studies showed that the transcript encoding the precursor is present in VD1, but not in RPD2, thus corroborating the single-cell MS analysis. Finally, the small cardioactive peptides were shown to enhance the contractions of the auricle in vitro.

Amino Acid Sequence↗
PubMed2001

Hydrazino peptides as foldamers: an extension of the beta-peptide concept.

Replacing the C(beta) atoms in the beta-amino acid constituents of beta-peptides by nitrogen atoms leads to hydrazino peptides. A systematic conformation analysis of blocked hydrazino peptide oligomers of the general type I at the HF/6-31G, MP2/6-31G, and DFT/B3LYP/6-31G levels of ab initio MO theory and on the basis of molecular mechanics reveals a wide variety of secondary structures, as for instance various helices and sheet- and turnlike conformers. Some of them are closely related to secondary structure types found in beta-peptides; others represent novel types. Thus, a very stable, novel helix with 14-membered hydrogen-bonded pseudocycles, which occupies a conformation space different from that of helices with 14-membered rings found among the most stable conformers in beta-peptides, is indicated. The most important secondary structure elements are characterized by interactions between peptidic NH and CO groups. The additional hydrazino N(alpha)H group takes part in special structuring effects but is of lesser importance for secondary structure formation. The influence of environmental effects on the existence and stability of the various structure types is discussed. Due to the wide variety of structural possibilities, hydrazino peptides might be a useful tool for peptide and protein design.

Hydrazines↗
PubMed2004

Partitioning of dual-lipidated peptides into membrane microdomains: lipid sorting vs peptide aggregation.

The lateral membrane organization and phase behavior of the lipid mixture DMPC(di-C(14))/DSPC(di-C(18))/cholesterol (0-33 mol %) with and without an incorporated fluorescence-labeled palmitoyl/farnesyl dual-lipidated peptide, BODIPY-Gly-Cys(Pal)-Met-Gly-Leu-Pro-Cys(Far)-OMe, which represents a membrane recognition model system for Ras proteins, was studied by two-photon excitation fluorescence microscopy. Measurements were performed on giant unilamellar vesicles (GUVs) over a large temperature range, ranging from 30 to 80 degrees C to cover different lipid phase states (all-gel, fluid/gel, liquid-ordered, all-fluid). At temperatures where the fluid-gel coexistence region of the pure binary phospholipid system occurs, large-scale concentration fluctuations appear. Incorporation of cholesterol levels up to 33 mol % leads to a significant increase of conformational order in the membrane system and a reduction of large domain structures. Adding the peptide leads to dramatic changes in the lateral organization of the membrane. With cholesterol present, a phase separation is induced by a lipid sorting mechanism owing to the high affinity of the lipidated peptide to a fluid, DMPC-rich environment. This phase separation leads to the formation of peptide-containing domains with high fluorescence intensity that become progressively smaller with decreasing temperature. As a result, the local concentration of the peptide increases steadily within the confines of the shrinking domains. At the lowest temperatures, where the acyl-chain order parameter of the membrane has already drastically increased and the membrane achieves a liquid-ordered character, an efficient lipid sorting mechanism is no longer supported and aggregation of the peptide into small clusters prevails. We can conclude that palmitoyl/farnesyl dual-lipidated peptides do not associate with liquid-ordered or gel-like domains in phase-separated bilayer membranes. In particular, the study shows the interesting ability of the peptide to induce formation of fluid microdomains at physiologically relevant cholesterol concentrations, and this effect very much depends on the concentration of fluid vs ordered lipid molecules.

Cholesterol↗
PubMed1996

Molecular recognition of peptide and non-peptide ligands by the extracellular domains of neurohypophysial hormone receptors.

This study was designed to ascertain whether the extracellular loops of vasopressin/oxytocin receptors bind ligands and, if so, to locate the molecular determinants of this ligand-receptor interaction. Ligand-binding studies were employed using a rat liver V1a vasopressin receptor preparation and both peptide and non-peptide receptor ligands. Synthetic peptides corresponding to defined regions of the extracellular surface of the neurohypophysial hormone receptors recognized radioligands. These receptor mimetics inhibited the binding of radioligands to the V1a receptor with apparent affinities (pKi) ranging from 3.1 to 6.75. The same mimetics had no effects on the binding of angiotensin II to the rat AT1 receptor, indicating specificity for V1a receptor ligands. A mimetic peptide (DITYRFRGPDWL) of the first extracellular loop (ECII) of the V1a vasopressin receptor also inhibited vasopressin-stimulated, but not angiotensin II-stimulated, glycogen phosphorylase in isolated rat hepatocytes. In contrast, scrambled ECII mimetics displayed greatly reduced affinity for vasopressin. In addition, the role of peptide side-chain versus main-chain atoms in the binding of ligands by vasopressin receptors was addressed using retro-inverso peptide mimetics. Our findings indicate a precise orientation of the extracellular receptor surface (particularly the ECII domain) which facilitates the initial 'capture' of both peptide and non-peptide ligands. Moreover, the data indicate that the main-chain atoms of both a major binding-site determinant in the first extracellular loop of the receptor and the neurohypophysial hormones contribute significantly to the ligand-receptor interaction. These findings also suggest that soluble receptor-binding domains have therapeutic potential.

Amino Acid Sequence↗
PubMed1997

The three-dimensional structure of an H-2Ld-peptide complex explains the unique interaction of Ld with beta-2 microglobulin and peptide.

Solution at 2.5-A resolution of the three-dimensional structure of H-2Ld with a single nine-residue peptide provides a structural basis for understanding its unique interaction with beta-2 microglobulin (beta2m) and peptide. Consistent with the biological data that show an unusually weak association of Ld with beta2m, a novel orientation of the alpha1/alpha2 domains of Ld relative to beta2m results in a dearth of productive contacts compared with other class I proteins. Characteristics of the Ld antigen-binding cleft determine the unique motif of peptides that it binds. Ld has no central anchor residue due to the presence of several bulky side chains in its mid-cleft region. Also, its cleft is significantly more hydrophobic than that of the other class I molecules for which structures are known, resulting in many fewer H-bonds between peptide and cleft residues. The choice of Pro as a consensus anchor at peptide position 2 appears to be related to the hydrophobicity of the B pocket, and to the unique occurrence of Ile (which mirrors Pro in its inability to form H-bonds) at position 63 on the edge of this pocket. Thus, the paucity of stabilizing H-bonds combined with poor complementarity between peptide postion 2 Pro and the B pocket contribute to the weak association between Ld and its peptide antigen. The unique structural interactions of Ld with beta2m and peptide could make Ld more suited than other classical class I molecules to play a role in alternative pathways of antigen presentation.

Animals↗
PubMed2004

Competition for access to the rat major histocompatibility complex class I peptide-loading complex reveals optimization of peptide cargo in the absence of transporter associated with antigen processing (TAP) association.

Major histocompatibility complex (MHC) class I molecules load peptides in the endoplasmic reticulum in a process during which the peptide cargo is normally optimized in favor of stable MHC-peptide interactions. A dynamic multimolecular assembly termed the peptide-loading complex (PLC) participates in this process and is composed of MHC class I molecules, calreticulin, ERp57, and tapasin bound to the transporter associated with antigen processing (TAP) peptide transporter. We have exploited the observation that the rat MHC class I allele RT1-Aa, when expressed in the rat C58 thymoma cell line, effectively competes and prevents the endogenous RT1-Au molecule from associating with TAP. However, stable RT1-Au molecules are assembled efficiently in competition with RT1-Aa, demonstrating that cargo optimization can occur in the absence of TAP association. Defined mutants of RT1-Aa, which do not allow formation of the PLC, fail to become thermostable in C58 cells. Wild-type RT1-Aa, which does allow PLC formation, also fails to become thermostable in this cell line, which carries the rat TAPB transporter that supplies peptides incompatible for RT1-Aa binding. Full optimization of RT1-Aa requires the presence of the TAP2A allele, which is capable of supplying suitable peptides. Thus, formation of the PLC alone is not sufficient for optimization of the MHC class I peptide cargo.

Animals↗