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PubMed1993

Further identification of bioactive peptides in the anterior byssus retractor muscle of Mytilus: two contractile and three inhibitory peptides.

1. Two contractile and three inhibitory peptides were newly isolated from the anterior byssus retractor muscles (ABRMs) of the bivalve mollusc Mytilus edulis by using the muscle as the bioassay system. 2. The structures of the two contractile peptides were GPFGTHIKamide (GPFG-8) and GPFGLNKHGamide (GPFG-9). The contractile response of the ABRM to the first-time application of GPFG-8 or GPFG-9 was of considerable size. The threshold concentrations of the peptides were around 10(-9) M. However, the contractile response to the second-time application was far smaller than that to the first-time application in both cases. Namely, the muscle showed tachyphylaxis to the peptides. 3. Two of the three inhibitory peptides were members of the Mytilus-inhibitory-peptide (MIP) family. Their structures were RAPLFIamide (MIP6) and RSPMFVamide (MIP7). The peptides, as well as the other MIPs previously identified, showed a potent inhibitory effect on phasic contraction of the ABRM in response to repetitive electrical stimulation. The remaining one was an MIP-related peptide (MIP-RP) having the sequence of MRYFVamide. The MIP-RP was less potent than the two MIPs in inhibiting the contraction of the ABRM.

Amino Acid Sequence↗
PubMed2005

Effect of NaCl and peptide concentration on the self-assembly of an ionic-complementary peptide EAK16-II.

Previous work has examined the effects of such factors as pH and peptide concentration on the self-assembly of ionic-complementary peptides. This work focused on the effect of sodium chloride on the molecular self-assembly of an ionic-complementary peptide EAK16-II (AEAEAKAKAEAEAKAK). Surface tensions and dimensions of the self-assembled nanostructures were determined for a wide range of peptide and sodium chloride concentrations using axisymmetric drop shape analysis-profile (ADSA-P) and atomic force microscopy (AFM), respectively. The critical aggregation concentration, or critical self-assembly concentration (CSAC), of EAK16-II was not significantly affected by the presence of NaCl. However, the analysis of size variations in self-assembled nanostructures in response to changes in NaCl concentration indicated that the presence of NaCl does influence the resulting dimensions of the peptide nanostructures when the peptide concentration is below its CSAC. A critical NaCl concentration was identified at approximately 20mM, below which the equivalent radius of the peptide fibrils increased with increasing salt concentration, and above which the opposite response was observed. This critical NaCl concentration was further confirmed in the surface tension measurements, where the equilibrium surface tension and induction time of the peptide at low concentrations (<CSAC) decreased with increasing NaCl concentration up to approximately 20mM and a further increase caused the opposite trend.

Amino Acid Sequence↗
PubMed2004

Detection of HIV-1-specific CTL responses in Clade B infection with Clade C Peptides and not Clade B consensus peptides.

The variability of HIV-1 sequences within and between persons in vivo complicates immunologic screening with a fixed sequence, and using peptides based on consensus sequences therefore has become a common practice for pathogenesis and vaccine studies. Here, we screen a cohort of HIV-1-infected persons in the United States for CD8+ T lymphocyte (CTL) responses using Gag peptides based on the Clade C primary isolate DU422 and the consensus sequence for Clade B. Surprisingly, the DU422 and Clade B consensus peptides are similar in sensitivity, but many responses are detected only by one set or the other. About equal numbers of discordantly detected responses are specific to consensus Clade B peptides as DU422 peptides. A minority of discordant detection is due to the varying frames of the peptide sets and therefore a technical artifact; the majority is due to sequence differences. This lack of superiority of the Clade B consensus peptides to detect CD8+ T lymphocyte responses is an unexpected finding that suggests that detection of HIV-1-specific cellular immunity with these peptides may be significantly insensitive and raises questions as to whether screening with a single sequence adequately reflects responses to the viral swarm in vivo.

Adult↗
PubMed2005

Peptide Tyrosine Arginine, a potent immunomodulatory peptide isolated and structurally characterized from the skin secretions of the dusky gopher frog, Rana sevosa.

An octadecapeptide was isolated from the skin secretions of the dusky gopher frog (Rana sevosa) on the basis of histamine release from rat peritoneal mast cells. This peptide was purified to homogeneity by HPLC and found to have the following primary structure, YLKGCWTKSYPPKPCFSR, using both Edman degradation chemistry and peptide sequencing using high-resolution mass spectrometry (Q-TOF MS). The peptide, named peptide Tyrosine Arginine (pYR) shares 77.8% homology with peptide Leucine Arginine (pLR). The effects of the natural amidated peptide, non-amidated peptide and C-loop region of pYR on granulopoiesis and neutrophil apoptosis were investigated. All three analogues inhibited the early development of granulocyte macrophage colonies from bone marrow stem cells but did not induce apoptosis of the end stage granulocytes, the mature neutrophil. Thus, pYR is a novel member of an important and emerging new class of amphibian peptides with hemopoietic actions.

Amino Acid Sequence↗
PubMed2005

Synthetic peptide vaccination in cattle: induction of strong cellular immune responses against peptides derived from the Mycobacterium bovis antigen Rv3019c.

Fully synthetic peptide vaccines possess attractive cost and safety attributes. However, peptide vaccines that induce cell-mediated immunity require both selection of appropriate peptides and the development of adjuvant formulations supporting the induction of cellular immunity. An adjuvant formulation composed of emulsigen and the synthetic CpG motif containing ODN2007 was tested in cattle for its ability to induce cellular immunity after peptide vaccination, and compared to Rv3019c DNA vaccination. Peptides from the protective Mycobacterium bovis antigen Rv3019c were included into the vaccine on the basis of their frequent and strong recognition by T cells from M. bovis infected or BCG vaccinated cattle. Following peptide vaccination, strong IFN-gamma and proliferative T cell responses were observed. Proliferative, but no significant IFN-gamma responses were induced by DNA vaccination. Peptide vaccination boosted responses primed by DNA vaccination. In conclusion, emulsigen and CpG motif containing ODN constitute a promising adjuvant formulation to deliver peptides to veterinary species.

Animals↗
PubMed1997

Control of human luteal steroidogenesis: role of growth hormone-releasing hormone, vasoactive intestinal peptide, and pituitary adenylate cyclase-activating peptide.

OBJECTIVE: To examine the possible effect of growth hormone-releasing hormone (GHRH), vasoactive intestinal peptide, and pituitary adenylate cyclase-activating peptide on basal and hCG-stimulated P production by human luteal cells. DESIGN: Cultures of human luteal cells from the early and midluteal phase. SETTING: All corpora lutea were obtained from the Obstetrics and Gynecology Department of the Università Cattolica, a public care center. PATIENT(S): Ten nonpregnant women between 35 and 47 years of age underwent surgery for various nonendocrine disorders, such as leiomyomatosis. INTERVENTION(S): Corpora lutea were obtained at the time of hysterectomy. MAIN OUTCOME MEASURE(S): Luteal cells were incubated with GHRH, vasoactive intestinal peptide, and pituitary adenylate cyclase-activating peptide with or without hCG at different concentrations. RESULT(S): Pituitary adenylate cyclase-activating peptide stimulated P production in a dose- and time-dependent manner, whereas GHRH and vasoactive intestinal peptide did not affect luteal steroidogenesis. None of the three peptides were found to synergize with hCG. CONCLUSION(S): Pituitary adenylate cyclase-activating peptide can influence human luteal steroidogenesis.

Adult↗
PubMed2002

Novel biological activities of the fish pro-IGF-I E-peptides: studies on effects of fish pro-IGF-I E-peptide on morphological change, anchorage-dependent cell division, and invasiveness in tumor cells.

E-peptides of proinsulin-like growth factor-I (pro-IGF-I) are proteolytically cleaved from the prohormone after translation and have long been regarded as biologically inactive. Tian et al. [Endocrinology 140 (1999) 3387-3390] recently demonstrated that recombinant rainbow trout pro-IGF-I E-peptides (rtEa-2-, rtEa-3-, and rtEa-4-peptides), like hIGF-I, exhibited a dose-dependent mitogenic activity in several nontransformed mammalian cell lines. We show in this report that treatment of established human and fish cancer cells (MCF-7, HT-29, HepG2, ZR-75-1, SK-N-F1, and HC) and retroviral transformed human embryonic kidney cells (293GP) with recombinant rtEa-2- or rtEa-4-, but not rtEa-3-peptide, resulted in a dose-dependent induction of morphological change and enhanced cell attachment. The E-peptide-induced morphological changes are sensitive to treatment with alpha-amanitin or cycloheximide, known inhibitors of RNA and protein synthesis. The in vitro colony formation activity of established human tumor cells (HT-29 and MDA-MB-231) is greatly reduced or diminished by treatment with the rtEa-4-peptide. Both morphological change and reduction of colony formation activity in MDA-MB-231 cells were also observed following transfection with an Ea-4 transgene construct. Furthermore, the invasive activity of HT1080 cells, known invasive cancer cells, is reduced three to fourfold by treatment with the rtEa-4-peptide. These results suggest that E-peptides of rainbow trout pro-IGF-I possess novel biological activities controlling malignant properties of cancer cells in vitro.

Animals↗
PubMed1989

Strong cation-exchange high-performance liquid chromatography of peptides. Effect of non-specific hydrophobic interactions and linearization of peptide retention behaviour.

Strong cation-exchange chromatography (strong CEX) is probably the most useful mode of high-performance ion-exchange chromatography (IEC) for peptide separations. Although the hydrophobic character of high-performance ion-exchange packings, often giving rise to mixed-mode contributions to solute separations, has long been recognized, a systematic approach to examining the effect and magnitude of the hydrophobicity of these packings during IEC of peptides has so far been lacking. In the present study, we report the synthesis of three series of positively charged peptide polymers which vary significantly in overall hydrophobicity and polypeptide chain length (5-50 amino acid residues): Ac-(Gly-Lys-Gly-Leu-Gly)n-amide, Ac-(Leu-Gly-Leu-Lys-Ala)n-amide and Ac-(Leu-Gly-Leu-Lys-Leu)n-amide (n = 1, 2, 4 6, 8, 10). We have examined non-specific hydrophobic interactions of these peptides with both silica-and polymer-based ion-exchange packings, demonstrating how these interactions are overcome by the addition of acetonitrile to the mobile phase. It was also shown that removal of non-specific hydrophobic interactions may be necessary just to elute peptides from the ion-exchange matrix. In addition, from the observed retention times of these three peptide polymer series and other peptides which vary substantially in charge density, net charge, polypeptide chain length and hydrophobicity, we have established a simple approach to linearization and, thus, prediction of peptide retention behaviour in CEX.

Chromatography, High Pressure Liquid↗
PubMed1996

Inhibition of cell adhesion to the virus by synthetic peptides of fiber knob of human adenovirus serotypes 2 and 3 and virus neutralisation by anti-peptide antibodies.

The fiber knob of adenovirus (Ad) causes the first step in the interaction of adenovirus with cell membrane receptors. To obtain information on the receptor binding site(s) several synthetic peptides derived from Ad2 and Ad3 fiber head sequences and their antisera were tested for interference with virus attachment to HeLa and FL cells and cell adhesion to viruses. The anti-peptide sera were also evaluated in ELISA and virus neutralisation test. Ad2 (of subgroup C) and Ad3 (of subgroup B) attachment was not significantly inhibited by peptides corresponding to the amino acid residues 535-554, 555-573, 562-582 of Ad2 fiber or 210-225, 267-283, 291-306 and 300-319 of Ad3 fiber. However, microplate pre-adsorbed Ad3 fiber residues 210-225 and 267-283 could bind FL and HeLa cells, and 1 mg/ml of Ad3 fiber residues 267-283 inhibited the cell adhesion to Ad3 virus to approximately 90%. This peptide may participate in the receptor binding site of Ad3 fiber. ELISA reactive anti-peptide antibodies against the homologous peptide and virus did not significantly reduce the cell adhesion to the immobilised virus or the virus attachment to cells, but in the neutralisation assay antibodies raised to Ad2 fiber residues 555-573 and 562-582 and Ad3 fiber residues 210-225 caused neutralisation of the homologous virus at serum dilutions of 1:500 and 1:32, respectively. The corresponding peptides and one further peptide of Ad2 fiber and two of Ad3 fiber seem to contain neutralisation epitopes.

Adenoviruses, Human↗
PubMed1997

Peptide-specific CTL induction in HBV-seropositive PBMC by stimulation with peptides in vitro: novel epitopes identified from chronic carriers.

Cytotoxic T lymphocytes (CTL) recognize and destroy virus-infected cells, and it has been established that epitope-based peptides could induce such CTL in vivo as well as in vitro. In this study attempts were made to define the epitopes that are recognized by the CTL, and thus a series of 9- to 10-mer peptides derived from the amino acid sequences of hepatitis B virus (HBV) proteins were synthesized on the basis of the previously described HLA-A2 peptide binding motif. The binding assay of the synthetic peptides using transporter-associated with antigen processing (TAP)-deficient human cell line, T2, showed that eight out of 11 peptides tested enhanced the expression of HLA-A2 molecules on the T2 cell surface. Some of these peptides triggered activation of CTL in peripheral blood mononuclear cells of HBV-seropositive chronic carriers. The activated CTL in turn recognized and killed the T2 cells pulsed with the same peptides. This study shows that novel HLA-A2-restricted epitopes exist in the natural repertoire of immunity against HBV. These findings can be useful in developing peptide-based therapeutics against viral infections.

Carrier State↗
PubMed1998

Synthetic peptides of human papillomavirus type 18 E6 harboring HLA-A2.1 motif can induce peptide-specific cytotoxic T-cells from peripheral blood mononuclear cells of healthy donors.

To identify cytotoxic T-cell (CTL) epitopes against human papillomavirus type 18 (HPV 18) E6 protein that might be useful for developing peptide-based vaccine against HPV 18 infection, 18 peptides which possibly contain CTL epitopes were selected on the basis of previously described human leukocyte antigen (HLA)-A2.1-binding motif and chemically synthesized. In the binding assay of the synthetic peptides, 8 out of 18 synthetic peptides enhanced the expression of HLA-A2.1 molecules on T2 cell surface, which implies that these peptides were able to bind the HLA molecules. Those peptides having good binding affinity to HLA-A2.1 were tested for their ability to activate CTLs which were isolated from peripheral blood mononuclear cells (PBMCs) of healthy blood donors and to kill the target T2 cells pulsed with the same peptide. Five out of eight tested peptides activated CTLs and killed the target cells.

Binding Sites↗
PubMed1998

Binding affinity independent contribution of peptide length to the stability of peptide-HLA-DR complexes in live antigen presenting cells.

The effect of peptide length on the stability of peptide-HLR-DR1 (DR1) complexes was analyzed using two peptide series of increasing length, each containing a 7mer core with five DR1-binding anchors, extended stepwise with Ala residues at the N- and C-terminus, respectively. The Ala extensions, although did not affect binding affinity, significantly increased the half lives of peptide-DR1 complexes (from 1.5 h up to 10 h) in live antigen presenting cells (APC). Flanking residues from position -2 to 0 and 8 to 11 were involved in the affinity-independent increase of complex stability. The shortest (8mer and 9mer) peptides, with in vivo half lives of <2.5 h, were unable to form stable complexes with DR1 in presence of HLA-DM (DM) molecules, and were poor competitors of antigen presentation. Longer peptides were resistant to DM-mediated unloading, and were efficient competitors of antigen presentation. Thus, DM appears to limit short peptides in establishing biologically relevant DR occupancy, despite their high binding affinity. In APC, stable complexes can form only with high affinity peptides of >9 residues, and the longevity of complexes seems to depend on full of occupation of the binding site.

Antibodies, Monoclonal↗
PubMed2003

Human hemoglobin-derived peptides exhibit antimicrobial activity: a class of host defense peptides.

Hemoglobin is a known source of biologically active peptides with various functions. In the present study, we report for the first time the existence of natural processed hemoglobin fragments exhibiting antimicrobial activity in humans. Two antimicrobial hemoglobin-derived peptides were purified from a human placental peptide library by consecutive chromatographic steps tracking the maximum growth inhibitory activity against Escherichia coli BL21. These peptides, consisting of 17 and 36 amino acid residues, were identified as being C-terminal fragments of gamma-hemoglobin and beta-hemoglobin, respectively. The antimicrobial beta-hemoglobin fragment was also purified from lysed erythrocytes, demonstrating that proteolytic degradation of hemoglobin into small bioactive peptides already starts inside erythrocytes. The identified peptides inhibit the growth of Gram-positive and Gram-negative bacteria and yeasts in micromolar concentrations. Moreover, by LPS-binding, the beta-hemoglobin fragment reduces biological activity of endotoxins. In contrast, even at high concentrations, the identified antimicrobial hemoglobin peptides do not exhibit toxic activity on human primary blood cells. We conclude that antimicrobial hemoglobin-derived peptides could be important effectors of the innate immune response killing microbial invaders.

Anti-Bacterial Agents↗
PubMedDate not supplied

Capture of peptides with N-terminal serine and threonine: a sequence-specific chemical method for Peptide mixture simplification.

The objective of this study was to evaluate a sequence-specific chemistry for the ability to specifically capture peptides that contain N-terminal serine or threonine residues from mixtures. The first step is the oxidation of the 1,2-amino alcohol structure -CH(NH(2))CH(OH)- of peptides containing N-terminal serine or threonine with periodate. The newly formed aldehyde reacts with a labeling reagent containing a hydrazide, RCONHNH(2), to form a hydrazone-peptide conjugate, RCONHN=CH-peptide. Biotin-labeled conjugates can then be isolated by affinity purification with streptavidin. The method described in this report can be useful in simplifying the complex mixtures of peptides that are generated in typical proteomic analysis, where proteins are digested with trypsin and analyzed using liquid chromatography mass spectrometry data. The sequence-specific peptide selection not only reduces the complexity of digest mixtures, but also provides additional information for peptide identification. The targeted peptides are those that have either serine or threonine adjacent to a protease cleavage site. The sequence information should greatly aid in both database matching for protein identification and for de novo sequence determination.

Affinity Labels↗
PubMed1992

Identification of peptides from the adenine binding domains of ATP and AMP in adenylate kinase: isolation of photoaffinity-labeled peptides by metal chelate chromatography.

Photoaffinity labeling with azidoadenine nucleotides was used to identify peptides from the ATP and AMP binding domains on chicken muscle adenylate kinase. Competition binding studies and enzyme assays showed that the 8-azido analogues of Ap4A and ATP modified only the MgATP2- site of adenylate kinase, whereas the 2-azido analogue of ADP modified the enzyme at both the ATP and AMP sites. The positions of the two nucleotide binding sites on the enzyme were deduced by isolating and sequencing the modified peptides. Photolabeled peptides were isolated by a new procedure that used metal chelate chromatography to affinity purify the photolabeled peptides prior to final purification by reverse-phase HPLC. The sequences of the peptides that were photolabeled with the 8-azido analogues corresponded to residues K28-L44, T153-K166, and T125-E135 of the chicken muscle enzyme. The residues that were present in both tryptic- and Staphylococcus aureus V-8 protease-generated versions of these peptides were assigned to the ATP binding domain on the basis of selective photoaffinity labeling with the 8-azidoadenine analogues. These peptides and an additional peptide corresponding to positions I110-K123 were photolabeled with 2-N3ADP. Since I110-K123 was photolabeled by 2-N3ADP but not by 8-N3Ap4A, it was assigned to the AMP binding domain.

Adenine↗
PubMed1992

Induced peptide conformations in different antibody complexes: molecular modeling of the three-dimensional structure of peptide-antibody complexes using NMR-derived distance restraints.

Intramolecular interactions in bound cholera toxin peptide (CTP3) in three antibody complexes were studied by two-dimensional transferred NOE spectroscopy. These measurements together with previously recorded spectra that show intermolecular interactions in these complexes were used to obtain restraints on interproton distances in two of these complexes (TE32 and TE33). The NMR-derived distance restraints were used to dock the peptide into calculated models for the three-dimensional structure of the antibody combining site. It was found that TE32 and TE33 recognize a loop comprising the sequence VPGSQHID and a beta-turn formed by the sequence VPGS. The third antibody, TE34, recognizes a different epitope within the same peptide and a beta-turn formed by the sequence IDSQ. Neither of these two turns was observed in the free peptide. The formation of a beta-turn in the bound peptide gives a compact conformation that maximizes the contact with the antibody and that has greater conformational freedom than alpha-helix or beta-sheet secondary structure. A total of 15 antibody residues are involved in peptide contacts in the TE33 complex, and 73% of the contact area in the antibody combining site consists of the side chains of aromatic amino acids. A comparison of the NMR-derived models for CTP3 interacting with TE32 and TE33 with the previously derived model for TE34 reveals a relationship between amino acid sequence and combining site structure and function. (a) The three aromatic residues that interact with the peptide in TE32 and TE33 complexes, Tyr 32L, Tyr 32H, and Trp 50H, are invariant in all light chains sharing at least 65% identity with TE33 and TE32 and in all heavy chains sharing at least 75% identity with TE33. Although TE34 differs from TE32 and TE33 in its fine specificity, these aromatic residues are conserved in TE34 and interact with its antigen. Therefore, we conclude that the role of these three aromatic residues is to participate in nonspecific hydrophobic interactions with the antigen. (b) Residues 31, 31c, and 31e of CDR1 of the light chain interact with the antigen in all three antibodies that we have studied. The amino acids in these positions in TE34 differ from those in TE32 and TE33, and they are involved in specific polar interactions with the antigen. (c) CDR3 of the heavy chain varies considerably both in length and in sequence between TE34 and the two other anti-CTP3 antibodies. These changes modify the shape of the combining site and the hydrophobic and polar interactions of CDR3 with the peptide antigen.

Amino Acid Sequence↗
PubMed1983

Lanthanide-induced peptide folding: variations in lanthanide affinity and induced peptide conformation.

The present work has demonstrated the utility of the diamagnetic lanthanides lutetium and lanthanum as metal binding probes for a synthetic 13-residue fragment representing calcium binding site 3 of rabbit skeletal troponin C (residues 103-115). The peptide conformation induced by these metals was monitored by the proton magnetic resonance at 270 MHz. The peptide affinity for these rare earths is 50-400 times higher than that for calcium (KLu3+, 1.3 X 10(4) M-1; KLa3+, 1.1 X 10(5) M-1; KCa2+, 3 X 10(2) M-1) which is related to the change in cation charge from 2+ to 3+. The peptide conformation induced by the presence of La3+ generates a different 1H NMR spectrum than the one observed for the lutetium-saturated peptide. Thus, it appears that these metals do not fold the peptide into exactly the same conformation. The resonance shifts observed during the Lu3+ titration are much smaller than those seen in the case of La3+ addition. The fact that lutetium binds less tightly than lanthanum to the peptide may be linked directly or indirectly to the difference in ionic radius between these metals (Lu3+, 0.86 A; La3+, 1.03 A). This may in turn indicate that the peptide primary sequence encodes for some aspects of metal ion specificity. The 1H NMR results also demonstrate that glycine-108 adopts a restricted geometry in the absence of metal such that its two alpha-carbon protons are in different environments which are further affected by the addition of either metal. These observations support the concept that geometric constraints arising from the particular peptide folding pattern near this residue correlate with the highly conserved nature of this site of the EF hand. This position remains occupied by glycine in most EF hand domains with the exception of known distorted calcium binding sites present in intestine calcium binding proteins and S-100.

Amino Acid Sequence↗
PubMed2003

Interfacial anchor properties of tryptophan residues in transmembrane peptides can dominate over hydrophobic matching effects in peptide-lipid interactions.

Membrane model systems consisting of phosphatidylcholines and hydrophobic alpha-helical peptides with tryptophan flanking residues, a characteristic motif for transmembrane protein segments, were used to investigate the contribution of tryptophans to peptide-lipid interactions. Peptides of different lengths and with the flanking tryptophans at different positions in the sequence were incorporated in relatively thick or thin lipid bilayers. The organization of the systems was assessed by NMR methods and by hydrogen/deuterium exchange in combination with mass spectrometry. Previously, it was found that relatively short peptides induce nonlamellar phases and that relatively long analogues order the lipid acyl chains in response to peptide-bilayer mismatch. Here it is shown that these effects do not correlate with the total hydrophobic peptide length, but instead with the length of the stretch between the flanking tryptophan residues. The tryptophan indole ring was consistently found to be positioned near the lipid carbonyl moieties, regardless of the peptide-lipid combination, as indicated by magic angle spinning NMR measurements. These observations suggest that the lipid adaptations are not primarily directed to avoid a peptide-lipid hydrophobic mismatch, but instead to prevent displacement of the tryptophan side chains from the polar-apolar interface. In contrast, long lysine-flanked analogues fully associate with a bilayer without significant lipid adaptations, and hydrogen/deuterium exchange experiments indicate that this is achieved by simply exposing more (hydrophobic) residues to the lipid headgroup region. The results highlight the specific properties that are imposed on transmembrane protein segments by flanking tryptophan residues.

Alanine↗