Abstract
It has been shown that the minimal-length peptide having full stimulatory activity for pigeon cytochrome c-primed T cells from B10.A mice is composed of residues 88-103 of the moth (or 87-104 of the pigeon) sequence. However, to date, only residues 99-103(104)have been shown to be involved in contacting the T-cell receptor or the macrophage Ia molecule. Because the x-ray structure of tuna cytochrome c, and prior calculations on many homologous cytochrome c proteins, showed that segment 88-103(104) exists in the alpha-helical conformation, we postulate that residues 88-98 are necessary for maintaining the alpha-helical conformation of the COOH-terminal pentapeptide (99-103) involved in receptor recognition. To test this hypothesis, we have examined the conformational preferences of polypeptide segments from known antigenic regions near the carboxyl terminus of cytochrome c (pigeon, moth, and fly sequences) using conformational energy calculations for peptides in a nonpolar environment. We show here that fragments consisting of residues 88-91 and 94-98 of pigeon, moth, and fly cytochrome c have a strong alpha-helical preference, despite differences in sequence at residues 88-89 (Lys-Ala in pigeon, Ala-Asn in moth, and Pro-Asn in fly). In contrast, the tripeptide 91-93 (Arg-Ala-Asp) has a strong nonhelical preference. Furthermore, the COOH-terminal peptide 99-103 exists as a statistical coil. However, addition of residues 94-98 to residues 99-103 results in a peptide that has a strong preference for alpha-helix. From these computational results, we predict (i) that fragment 94-103, existing predominantly as an alpha-helix, should exhibit stimulatory activity and (ii) that the nonhelical peptide 91-93 can be deleted from fragment 88-103 without affecting its antigenicity. Both of these predictions have been borne out by experiments in which the two peptides were synthesized and shown to stimulate a T-cell proliferative response. These results establish a strong correlation between conformation (here, alpha-helix) and biological activity and suggest that T-cell activation is sensitive to the organized backbone structure that the antigen adopts in the nonpolar environment of the macrophage membrane or in the combining site of the T-cell receptor.
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- Dickerson R. E., Takano T., Eisenberg D., Kallai O. B., Samson L., Cooper A., Margoliash E. Ferricytochrome c. I. General features of the horse and bonito proteins at 2.8 A resolution. J Biol Chem. 1971 Mar 10;246(5):1511–1535. [PubMed] [Google Scholar]
- Hansburg D., Hannum C., Inman J. K., Appella E., Margoliash E., Schwartz R. H. Parallel cross-reactivity patterns of 2 sets of antigenically distinct cytochrome c peptides: possible evidence for a presentational model of Ir gene function. J Immunol. 1981 Nov;127(5):1844–1851. [PubMed] [Google Scholar]
- Lewis P. N., Scheraga H. A. Prediction of structural homology between bovine -lactalbumin and hen egg white lysozyme. Arch Biochem Biophys. 1971 Jun;144(2):584–588. doi: 10.1016/0003-9861(71)90364-x. [DOI] [PubMed] [Google Scholar]
- Lewis P. N., Scheraga H. A. Predictions of structural homologies in cytochrome c proteins. Arch Biochem Biophys. 1971 Jun;144(2):576–583. doi: 10.1016/0003-9861(71)90363-8. [DOI] [PubMed] [Google Scholar]
- Némethy G., Scheraga H. A. Protein folding. Q Rev Biophys. 1977 Aug;10(3):239–252. doi: 10.1017/s0033583500002936. [DOI] [PubMed] [Google Scholar]
- Pincus M. R., Klausner R. D. Prediction of the three-dimensional structure of the leader sequence of pre-kappa light chain, a hexadecapeptide. Proc Natl Acad Sci U S A. 1982 Jun;79(11):3413–3417. doi: 10.1073/pnas.79.11.3413. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Pincus M. R., Klausner R. D., Scheraga H. A. Calculation of the three-dimensional structure of the membrane-bound portion of melittin from its amino acid sequence. Proc Natl Acad Sci U S A. 1982 Aug;79(16):5107–5110. doi: 10.1073/pnas.79.16.5107. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Ploegman J. H., Drent G., Kalk K. H., Hol W. G. Structure of bovine liver rhodanese. I. Structure determination at 2.5 A resolution and a comparison of the conformation and sequence of its two domains. J Mol Biol. 1978 Aug 25;123(4):557–594. [PubMed] [Google Scholar]
- Scheraga H. A. Recent progress in the theoretical treatment of protein folding. Biopolymers. 1983 Jan;22(1):1–14. doi: 10.1002/bip.360220104. [DOI] [PubMed] [Google Scholar]
- Solinger A. M., Ultee M. E., Margoliash E., Schwartz R. H. T-lymphocyte response to cytochrome c. I. Demonstration of a T-cell heteroclitic proliferative response and identification of a topographic antigenic determinant on pigeon cytochrome c whose immune recognition requires two complementing major histocompatibility complex-linked immune response genes. J Exp Med. 1979 Oct 1;150(4):830–848. doi: 10.1084/jem.150.4.830. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Ultee M. E., Margoliash E., Lipkowski A., Flouret G., Solinger A. M., Lebwohl D., Matis L. A., Chen C., Schwartz R. H. The T lymphocyte response to cytochrome c--II. Molecular characterization of a pigeon cytochrome c determinant recognized by proliferating T lymphocytes of the B10.A mouse. Mol Immunol. 1980 Jul;17(7):809–822. doi: 10.1016/0161-5890(80)90030-9. [DOI] [PubMed] [Google Scholar]
- Zimmerman S. S., Pottle M. S., Némethy G., Scheraga H. A. Conformational analysis of the 20 naturally occurring amino acid residues using ECEPP. Macromolecules. 1977 Jan-Feb;10(1):1–9. doi: 10.1021/ma60055a001. [DOI] [PubMed] [Google Scholar]