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PubMed1992

Molecular thermodynamic model to predict the alpha-helical secondary structure of polypeptide chains in solution.

The native state of a protein molecule in aqueous solutions represents one of the lowest states of Gibbs energy [Anfinsen, C.B. (1973) Science 181, 223-230]. Much progress has been made about the rules of protein folding [King, J. (1989) Chem. Eng. News 67, 32-54] and the dominant forces in protein folding [Dill, K.A. (1990) Biochemistry 29, 7133-7155]. However, the quantitative contributions of different Gibbs energy terms to protein stability remains a controversial issue [Moult, J., & Unger, R. (1991) Biochemistry 30, 3816-3824]. A molecular thermodynamic model has been proposed for the Gibbs energy of folding a residue in aqueous homopolypeptides from a random-coiled state to either the alpha-helix state or the beta-sheet state [Chen, C.-C., Zhu, Y., King, J.A., & Evans, L.B. (1992) Biopolymers 32, 1375-1392]. In this work, we present a generalization of the molecular thermodynamic model for the Gibbs energy of folding natural and synthetic heteropolypeptides from random-coiled conformations into alpha-helical conformations. The generalized model incorporates the intrinsic folding potential due to residue-solvent interactions, the cooperative folding effect due to residue-residue interactions, and the location and length of alpha-helices. The utility of the model was demonstrated by examining the stability of alpha-helical conformations of a number of natural polypeptides including C-peptide (residues 1-13) and S-peptide (residues 1-20) of RNase A (bovine pancreatic ribonuclease A), the P alpha fragment in BPTI (bovine pancreatic trypsin inhibitor), and synthetic polypeptides (the copolymers of different amino acid residues) including alanine-based peptides (16 or 17 residues long) in water. The computed Gibbs energies correspond well with the experimental data on helicity. The results also accounted for the effects of amino acid substitution and temperature on the stability of alpha-helical conformations of the test polypeptides.

Amino Acid Sequence↗
PubMed1992

Fourier transform infrared analysis of bacteriorhodopsin secondary structure.

Fourier transform infrared spectroscopy at a resolution of 1 cm-1 has been used to study the conformation of dark-adapted bacteriorhodopsin in the native purple membrane, in H2O and D2O suspensions. A detailed analysis of the amide I bands was made using derivative and deconvolution techniques. Curve-fitting results of four independent experiments indicate, after estimation of the methodological errors, that native bacteriorhodopsin contains 52-73% alpha-helices, 13-19% reverse turns, 11-16% beta-sheets, and 3-7% unordered segments. Our analysis has enabled the identification of several components corresponding to alpha-helices, beta-sheets, and reverse turns. Besides the alpha I- and alpha II-helices (peaking at 1658 and 1665 cm-1), we propose that two more infrared bands arise from alpha-helical structures: one at 1650 cm-1 from alpha I and another one at 1642 cm-1 in H2O suspension, which could originate from type III beta-turns (i.e., one turn of 3(10)-helix). The relatively high content of reverse turns suggests the presence of one reverse turn per loop, plus another one in the C-terminal segment. On the other hand, several reasons argue that the calculated mean beta-sheet content of around 14% should be decreased somewhat. These beta-sheets could be located in the noncytoplasmatic links of the bacteriorhodopsin molecule.

Bacteriorhodopsins↗
PubMed1994

Unusual helix-containing greek keys in development-specific Ca(2+)-binding protein S. 1H, 15N, and 13C assignments and secondary structure determined with the use of multidimensional double and triple resonance heteronuclear NMR spectroscopy.

Multidimensional heteronuclear NMR spectroscopy has been used to determine almost complete backbone and side-chain 1H, 15N, and 13C resonance assignments of calcium loaded Myxococcus xanthus protein S (173 residues). Of the range of constant-time triple resonance experiments recorded, HNCACB and CBCA(CO)NH, which correlate C alpha and C beta with backbone amide resonances of the same and the succeeding residue respectively, proved particularly useful in resolving assignment ambiguities created by the 4-fold internal homology of the protein S amino acid sequence. Extensive side-chain 1H and 13C assignments have been obtained by analysis of HCCH-TOCSY and 15N-edited TOCSY-HMQC spectra. A combination of NOE, backbone amide proton exchange, 3JNH alpha coupling constant, and chemical shift data has been used to show that each of the protein S repeat units consists of four beta-strands in a Greek key arrangement. Two of the Greek keys contain a regular alpha-helix between the third and fourth strands, resulting in an unusual and possibly unique variation on this common folding motif. Despite similarity between two nine-residue stretches in the first and third domains of protein S and one of the Ca(2+)-binding sequences in bovine brain calmodulin [Inouye, S., Franceschini, T., & Inouye, M. (1983) Proc. Natl. Acad. Sci. U.S.A. 80, 6829-6833], the protein S topology in these regions is incompatible with an EF-hand calmodulin-type Ca(2+)-binding site.

Amino Acid Sequence↗
PubMed1994

Identifying the lipid-protein interface of the Torpedo nicotinic acetylcholine receptor: secondary structure implications.

To identify amino acid residues of the Torpedo nicotinic acetylcholine receptor (AchR) interacting with membrane lipid, we have used the photoactivatable, hydrophobic probe 3-trifluoromethyl-3-(m-[125I]-iodophenyl)diazirine([125I]TID). The pattern of [125I]TID incorporation into the M3 and M4 hydrophobic segments of each subunit was the same both in the presence and absence of the agonist carbamoylcholine and in the presence of an excess of nonradioactive TID, consistent with nonspecific photoincorporation from the lipid-protein interface. [125I]TID reacted with five residues in alpha-M4 [Blanton, M.P., & Cohen, J. B. (1992) Biochemistry 31, 3738-3750] but with only two or three residues in M4 segments of beta-, gamma-, and delta-subunits. In delta-M3, [125I]TID reacted with Met-293, Ser-297, Gly-301, Val-304, and Asn-305 as well as with Ile-288 preceding M3. Residues at corresponding positions were labeled in beta-M3 (Met-285, Ile-289, Phe-293) and in gamma-M3 (Phe-292, Leu-296, Met-299, and Asn-300) as well as gamma-Ile-283. Within alpha-M3, Phe-284 and Ser-287 were labeled. The periodicity of labeled residues provides the first direct evidence that M3 as well as M4 segments of each subunit are organized as transmembrane alpha-helices each with substantial contact with lipid. In addition, in alpha-M1 [125I]TID reacted nonspecifically with Cys-222, Leu-223, Phe-227, and Leu-228, a pattern of incorporation inconsistent with the labeling pattern expected either for a "face" of an alpha-helix or a beta-sheet.

Amino Acid Sequence↗
PubMed1994

Multinuclear, multidimensional NMR studies of Anabaena 7120 heterocyst ferredoxin. Sequence-specific resonance assignments and secondary structure of the oxidized form in solution.

Sequence-specific assignments were determined for the diamagnetic proton resonances from recombinant Anabaena 7120 heterocyst ferredoxin (M(r) = 11,000) produced in Escherichia coli. Several samples selectively labeled with nitrogen-15 were prepared for use in two-dimensional heteronuclear multiple quantum coherence (HMQC) [Müller, L. (1979) J. Am. Chem. Soc. 101, 4481-4484] experiments. A sample uniformly labeled with nitrogen-15 was also prepared and used in two three-dimensional experiments: NOESY-HMQC and TOCSY-HMQC [Zuiderweg, E. R. P., & Fesik, S. W. (1989) Biochemistry 28, 2387-2391; Marion, D., Ikura, M., Tsuchudin, R., & Bax, A. (1989) J. Magn. Reson. 85, 393-399]. The sequential assignment strategy relied on the detection of 15N-edited interresidue 1H alpha i/1HNi+1 NOE connectivities. Starting points and checks were provided by HMQC spectra of the selectively labeled samples. A sample doubly labeled with carbon-13 and nitrogen-15 was also prepared and used in three triple-resonance experiments: HNCA, HNCO, and HN(CO)CA [Ikura, M., Kay, L. E., & Bax, A. (1990) Biochemistry 29, 4659-4667; Kay, L. E., Ikura, M., Tschudin, R., & Bax, A. (1990) J. Magn. Reson. 89, 496-514]. The HNCA and HN(CO)CA spectra, which were used to confirm assignments from NOE connectivities, provided independent sequential assignments from spin couplings. Resonances from 18 residues were not seen in the diamagnetic region of the NMR spectrum. Several of these residues are very close to the [2Fe-2S] cluster, and their absence is explained by paramagnetic broadening and/or shifting.(ABSTRACT TRUNCATED AT 250 WORDS)

Anabaena↗
PubMed1994

Synthetic S-2 and H-5 segments of the Shaker K+ channel: secondary structure, membrane interaction, and assembly within phospholipid membranes.

Current models of voltage-activated K+ channels predict that the channels are formed by the coassembly of four polypeptide monomers, each of which consists of six transmembrane segments (S1-S6) and long terminal domains. The aqueous pores are thought to be composed of the conserved H-5 regions contributed by four monomers. In this study, two putative membrane-embedded segments of the Shaker K+ channel were synthesized. One segment corresponds to the putative, transmembrane helix S-2 (amino acids 275-300), and the other corresponds to the highly conserved 12 amino acid residues within the H-5 region [amino acids 432-443, designated (12)H-5]. Structural and functional characterization at elevated lipid/peptide molar ratios (> 3000:1) was performed on the two segments, as well as on a previously synthesized 21 amino acid long peptide with a sequence resembling the entire H-5 region (designated (21)H-5) (Peled & Shai, 1993). Circular dichroism spectroscopy revealed that S-2 adopts predominantly alpha-helical structure in both trifluoroethanol and 35 mM SDS (78% or 99%, respectively), while (12)H-5 and (21)H-5 adopt low alpha-helical structure only in the presence of 35 mM SDS. Functional characterization demonstrated that S-2 and (12)H-5 segments bind to zwitterionic phospholipids, with partition coefficients on the order of 10(4) M-1. Resonance energy transfer measurements, between donor/acceptor-labeled pairs of peptides, revealed that the peptides self-associate in their membrane-bound state, which may correlate with the existence of functional interactions between the conserved (12)H-5 regions of different subunits of K+ channels (Kirsch et al., 1993).(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1993

Secondary structure and zinc ligation of human recombinant short-form stromelysin by multidimensional heteronuclear NMR.

Stromelysin-1, a member of the matrix metalloendoprotease family, is a zinc protease involved in the degradation of connective tissue in the extracellular matrix. As a step toward determining the structure of this protein, multidimensional heteronuclear NMR experiments have been applied to an inhibited truncated form of human stromelysin-1. Extensive 1H, 13C, and 15N sequential assignments have been obtained with a combination of three- and four-dimensional experiments. On the basis of sequential and short-range NOEs and 13C alpha chemical shifts, two helices have been delineated, spanning residues Asp-111 to Val-127 and Leu-195 to Ser-206. A third helix spanning residues Asp-238 to Gly-247 is characterized by sequential NOEs and 13C alpha chemical shifts, but not short-range NOEs. The lack of the latter NOEs suggests that this helix is either distorted or mobile. Similarly, sequential and interstrand NOEs and 13C alpha chemical shifts characterize a four-stranded beta-sheet with three parallel strands (Arg-100 to Ile-101, Ile-142 to Ala-147, Asp-177 to Asp-181) and one antiparallel strand (Ala-165 to Tyr-168). Two zinc sites have been identified in stromelysin [Salowe et al. (1992) Biochemistry 31, 4535-4540]. The NMR spectral properties, including chemical shift, pH dependence, and proton coupling of the imidazole nitrogens of six histidine residues (151, 166, 179, 201, 205, and 211), invariant in the matrix metalloendoprotease family, suggest that these residues are zinc ligands. NOE data indicate that these histidines form two clusters: one ligates the catalytic zinc (His-201, -205, and -211), and the other ligates a structural zinc (His-151, -166, and -179). Heteronuclear multiple quantum correlated spectra and specific labeling experiments indicate His-151, -179, -201, -205, and -211 are in the N delta 1H tautomer and His-166 is in the N epsilon 2H tautomer.

Amino Acid Sequence↗
PubMed1994

Purification, bioactivity, and secondary structure analysis of mouse and human macrophage migration inhibitory factor (MIF).

The cytokine macrophage migration inhibitory factor (MIF) has been identified to be secreted by the pituitary gland and the monocyte/macrophage and to play an important role in endotoxic shock. Despite the recent molecular cloning of a human T-cell MIF, characterization of the biochemical and biological properties of this protein has remained incomplete because substantial quantities of purified, recombinant, or native MIF have not been available. We describe the cloning of mouse MIF from anterior pituitary cells (AtT-20) and the purification of native MIF from mouse liver by sequential ion exchange and reverse-phase chromatography. For comparison purposes, human MIF was cloned from the Jurkat T-cell line and also characterized. Mouse and human MIF were highly homologous (90% identity over 115 amino acids). Recombinant mouse and human MIF were expressed in Escherichia coli and purified in milligram quantities by a simple two-step procedure. The molecular weight of native mouse MIF (12.5 kDa monomer) was identical with that of recombinant mouse MIF as assessed by gel electrophoresis and mass spectroscopy. No significant post-translational modifications were detected despite the presence of two potential N-linked glycosylation sites. Recombinant MIF inhibited monocyte migration in a dose-dependent fashion, and both recombinant and native MIF-exhibited comparable biological activities. MIF induced the secretion of tumor necrosis factor-alpha and stimulated nitric oxide production by macrophages primed with interferon-gamma. Circular dichroism spectroscopy revealed that bioactive mouse and human MIF exhibit a highly ordered, three-dimensional structure with a significant percentage of beta-sheet and alpha-helix conformation. Guanidine hydrochloride-induced unfolding experiments demonstrated that MIF is of low to moderate thermodynamic stability. These studies establish the biochemical identity of native and recombinant MIF and provide a first insight into the three-dimensional structural properties of this critical inflammatory mediator.

Amino Acid Sequence↗
PubMed2002

Secondary structure and lipid interactions of the N-terminal segment of pulmonary surfactant SP-C in Langmuir films: IR reflection-absorption spectroscopy and surface pressure studies.

Pulmonary surfactant, a thin lipid/protein film lining mammalian lungs, functions in vivo to reduce the work of breathing and to prevent alveolar collapse. Analogues of two hydrophobic surfactant proteins, SP-B and SP-C, have been incorporated into therapeutic agents for respiratory distress syndrome, a pathological condition resulting from deficiency in surfactant. To facilitate rational design of therapeutic agents, a molecular level understanding of lipid interaction with surfactant proteins or their analogues in aqueous monolayer films is necessary. The current work uses infrared reflection-absorption spectroscopy (IRRAS) to determine peptide conformation and the effects of S-palmitoylation on the lipid interactions of a synthetic 13 residue N-terminal peptide [SP-C13(palm)(2)] of SP-C, in mixtures with 1,2-dipalmitoylphosphatidylcholine (DPPC) or 1,2-dipalmitoylphosphatidylglycerol (DPPG). Two Amide I' features, at approximately 1655 and approximately 1639 cm(-1) in the peptide IRRAS spectra, are assigned to alpha-helical peptide bonds in hydrophobic and aqueous environments, respectively. In binary DPPC/SP-C13(palm)(2) films, the proportion of hydrated/hydrophobic helix increases reversibly with surface pressure (pi), suggestive of the peptide being squeezed out from hydrophobic regions of the monolayer. No such effect was observed for DPPG/peptide monolayers, indicative of stronger, probably electrostatic, interactions. Depalmitoylation produced a weakened interaction with either phospholipid as deduced from IRRAS spectra and from pi-area isotherms. S-Palmitoylation may modulate peptide hydration and conformation in the N-terminal region of SP-C and may thus permit the peptide to remain in the film at the high surface pressures present during lung compression. The unique capability of IRRAS to detect the surface pressure dependence of protein or peptide structure/interactions in a physiologically relevant model for surfactant is clearly demonstrated.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed2002

Ligand-induced differences in secondary structure of the Vibrio parahaemolyticus Na+/galactose cotransporter.

A detailed structural study of the prokaryotic sodium/galactose transporter (vSGLT) from Vibrio parahaemolyticus using attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy reveals stepwise increases in alpha-helicity upon binding of sodium and D-galactose. These increases in helicity correlate with decreases in beta-structural elements. The changes are accompanied by stepwise reductions in the degree of H/D exchange (HDX), suggesting reduced accessibility of water to the protein backbone. The data demonstrate discrete conformational changes from one intermediate to the next during the catalytic cycle of the protein and are interpreted in a model of the symport reaction mechanism.

Amides↗
PubMed2005

Hydrogen-deuterium (H/D) exchange mapping of Abeta 1-40 amyloid fibril secondary structure using nuclear magnetic resonance spectroscopy.

We describe here details of the hydrogen-deuterium (H/D) exchange behavior of the Alzheimer's peptide Abeta(1)(-)(40), while it is a resident in the amyloid fibril, as determined by high-resolution solution NMR. Kinetics of H/D exchange in Abeta(1)(-)(40) fibrils show that about half the backbone amide protons exchange during the first 25 h, while the other half remain unexchanged because of solvent inaccessibility and/or hydrogen-bonded structure. After such a treatment for 25 h with D(2)O, fibrils of (15)N-enriched Abeta were dissolved in a mixture of 95% dimethyl sulfoxide (DMSO) and 5% dichloroacetic acid (DCA) and successive heteronuclear (1)H-(15)N HSQC spectra were collected to identify the backbone amides that did not exchange in the fibril. These studies showed that the N and C termini of the peptide are accessible to the solvent in the fibril state and the backbone amides of these residues are readily exchanged with bulk deuterium. In contrast, the residues in the middle of the peptide (residues 16-36) are mostly protected, suggesting that that many of the residues in this segment of the peptide are involved in a beta structure in the fibril. Two residues, G25 and S26, exhibit readily exchangeable backbone amide protons and therefore may be located on a turn or a flexible part of the peptide. Overall, the data substantially supports current models for how the Abeta peptide folds when it engages in the amyloid fibril structure, while also addressing some discrepancies between models.

Amyloid beta-Peptides↗
PubMed2005

Secondary structure formation of a transmembrane segment in Kv channels.

Transmembrane segments in the intact voltage-gated potassium (Kv) channel are helical. To ascertain whether this helicity could first be manifested inside the ribosomal tunnel, we generated biogenic peptide intermediates of Kv1.3 and mass-tagged the cysteine-scanned S6 transmembrane segment using pegylation (PEG-MAL) and calmodulation (CaM-MAL). For reference, we created an extended peptide that was used as a "molecular tape measure" of the ribosomal tunnel and determined that the functional length of the tunnel is 99-112 A. We demonstrate that the S6 segment forms a compact structure inside the ribosomal tunnel and that the N-terminal half of S6 compacts more than the C-terminal half of S6. These results bear on the earliest folding events during biogenesis of ion channels.

Amino Acid Sequence↗
PubMed1999

Secondary structure and oligomerization behavior of equilibrium unfolding intermediates of the lambda cro repressor.

The thermal unfolding of the wild-type Cro repressor, its disulfide-bridged mutant Cro-V55C (with the Val-55 --> Cys single amino acid substitution), and a CNBr-fragment (13-66)2 of Cro-V55C was studied by Fourier transform infrared spectroscopy and dynamic light scattering. The combined approach reveals that thermal denaturation of Cro-WT and Cro-V55C proceeds in two steps through equilibrium unfolding intermediates. The first thermal transition of the Cro-V55C dimer involves the melting of the alpha-helices and the short beta-strand localized in the N-terminal part of the molecule. This event is accompanied by the formation of tetramers, and also impacts on the hydrogen-bonding interactions of the C-terminal beta-strands. The beta-sheet formed by the C-terminal parts of each polypeptide chain is the major structural feature of the intermediate state of Cro-V55C and unfolds during a second thermal transition, which is accompanied by the dissociation of the tetramers. Cutting of 12 amino acids in the N-terminal region is sufficient to prevent the formation of alpha-helical structure in the CNBr-fragment of Cro-V55C, and to induce tetramerization already at room temperature. The tetramers may persist over a broad temperature range, and start to dissociate only upon thermal unfolding of the beta-sheet structure formed by the C-terminal regions. The wild-type protein is a dimer at room temperature and at protein concentrations of 1.8-5.8 mg/mL. At lower concentrations, the dimers are stable until the onset of thermal unfolding, which is accompanied by the dissociation of the dimers into monomers. At higher protein concentrations, the unfolding is more complex and involves the formation of tetramers at intermediate temperatures. At these intermediate temperatures, the Cro-WT has lost all of its alpha-helical structure and also most of its native beta-sheet structure. Upon further temperature increase, a tendency for an intermolecular association of the beta-strands is observed, which may result in irreversible beta-aggregation at high protein concentrations.

Amino Acid Substitution↗
PubMedDate not supplied

X-ray evidence for a "super"-secondary structure in silk fibers.

X-ray studies on degummed B. mori silk fibers and on hydrogels prepared under a variety of conditions reveal moderately small angle reflections. These reflections are often highly oriented and are correlated to silk II lattice reflections. A superstructure can explain these features. Silk fibroin hydrogels were monitored as they dried to form the silk II structure. The silk II wide angle and moderately small angle patterns obtained from dried hydrogels and silk fibers are identical. The "superstructure" reflections at moderately small angle (3-7 nm) were first to appear, followed by the "intersheet" spacing, and then the remainder of the silk II wide angle scattering pattern. Thus, any superstructure hypothesized for the hydrogels (and for Silk II in fibers) must be both stable in a highly hydrated environment and must convert to silk II with little large scale diffusion. A folded structure, similar to amyloids and cross-beta-sheets but with much longer beta-strand stems, is proposed for silk II in fibers.

Animals↗
PubMedDate not supplied

Secondary structures and conformational changes in flagelliform, cylindrical, major, and minor ampullate silk proteins. Temperature and concentration effects.

Orb weaver spiders use exceptionally complex spinning processes to transform soluble silk proteins into solid fibers with specific functions and mechanical properties. In this study, to understand the nature of this transformation we investigated the structural changes of the soluble silk proteins from the major ampullate gland (web radial threads and spider safety line); flagelliform gland (web sticky spiral threads); minor ampullate gland (web auxiliary spiral threads); and cylindrical gland (egg sac silk). Using circular dichroism, we elucidated (i) the different structures and folds for the various silk proteins; (ii) irreversible temperature-induced transitions of the various silk structures toward beta-sheet-rich final states; and (iii) the role of protein concentration in silk storage and transport. We discuss the implication of these results in the spinning process and a possible mechanism for temperature-induced beta-sheet formation.

Amino Acids↗
PubMedDate not supplied

Effects of electrospinning and solution casting protocols on the secondary structure of a genetically engineered dragline spider silk analogue investigated via Fourier transform Raman spectroscopy.

Micrometer and submicrometer diameter fibers of recombinant dragline spider silk analogues, synthesized via protein engineering strategies, have been electrospun from 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) and compared with cast films via Raman spectroscopy in order to assess changes in protein conformation that may result from the electrospinning process. Although the solvent casting process was shown to result in predominantly beta-sheet conformation similar to that observed in the bulk, the electrospinning process causes a major change in conformation from beta-sheet to alpha-helix. A possible mechanism involving electric field-induced stabilization of alpha-helical segments in HFIP solution during the electrospinning process is discussed.

Amino Acid Sequence↗
PubMedDate not supplied

Aza-amino acid scanning of secondary structure suited for solid-phase peptide synthesis with fmoc chemistry and aza-amino acids with heteroatomic side chains.

Aza-peptides, peptide analogues in which the alpha-carbon of one or more of the amino acid residues is replaced with a nitrogen atom, exhibit a propensity for adopting beta-turn conformations. A general Fmoc-protection protocol for the stepwise solid-phase synthesis of aza-peptides has now been developed based on the activation of N'-alkyl fluoren-9-ylmethyl carbazates with phosgene for coupling the aza-amino acid residues. This method has proven effective for introducing aza-amino acid residues with aliphatic (Ala, Leu, Val, and Gly) and aromatic (Phe, Tyr, and Trp) side chains. Acid promoted loss of aromatic side chains was noted with aza-Trp and aza-Tyr residues during peptide cleavage and suppressed by temperature control in the case of the latter. In addition, aza-peptides with heteroatomic side chain residues (Lys, Orn, Arg, and Asp) were conveniently synthesized using this protocol. Partial aza-amino acid scans were performed on three biologically active peptides: the potent tetrapeptide melanocortin receptor agonist, Ac-His-d-Phe-Arg-Trp-NH2; the growth hormone secretagogue hexapeptide, GHRP-6, His-d-Trp-Ala-Trp-d-Phe-Lys-NH2; and the human calcitonin gene-related peptide (hCGRP) antagonist, FVPTDVGPFAF-NH2. This practical procedure for aza-amino acid scanning using Fmoc-based solid-phase synthesis should find general utility for probing the existence and importance of beta-turn conformations in bioactive peptides.

Amino Acid Sequence↗