We are interested in the relationship of peptide structure to biological function. Our general approach is to use spectroscopy and molecular dynamics simulations to characterize a compound of interest and to make predictions about the structure of analogs. We then synthesize these analogs, and employ spectroscopy, computer simulations and biological assays to develop structure/biological activity relationships. We have successfully modelled the beta-turn using various sequences of D- and L-glutamate and D- and L-lysine with lactam bridges to restrict backbone mobility. We are complementing this work with similar studies involving lactone bridges. This should distinguish the general conformational effects of structural constraints from those which are bridge-specific. Our molecular dynamics simulations of the lactone bridged compounds have already suggested a model for he gamma-turn. We intend to continue these simulations, and to synthesize the most promising compounds for spectroscopic measurements. In addition, we will synthesize polymers of our reverse-turn tetrapeptide units. The linear forms of the thymopoetin pentapeptide analogs, TP-5 and SP-5, are promoters of lymphocyte differentiation. We have performed molecular dynamics simulations and NMR spectroscopy on linear and bridged forms of TP-5, and are beginning simulations of the linear and bridged forms of SP-5. Dr. George Heavner or Ortho Pharmaceutical Co. is presently synthesizing both forms of SP-5, and we will begin spectroscopy as soon as the compounds are received. Studies of the biological activity of the bridged forms of both analogs are also underway in Dr. Heavner's laboratory. We are attempting to characterizing the conformations of nisin, a naturally-occurring, 34 amino acid peptide antibiotic. Nisin contains some unusual constituents: alpha, beta, unsaturated amino acids, and lanthionine (monosulfide) bridges. Although rare, these same constituents are also found in other naturally-occurring antibiotics, which suggests that they play a role in the biological activity. The lanthionine bridges also serve to constrain the molecule, which facilities both spectroscopic studies and molecular dynamics simulations. We have already carried out initial NMR spectorscopic measurements and molecular dynamics simulations, for both in vacuo and hydrated conditions, on certain synthetic fragments. These results will serve as a starting point for characterizing larger, biologically active fragments of nisin, and for a major effort to study the 3-D structure of the entire molecule. Such a program will entail extensive computer simulations, and broad application of NMR techniques such as NOESY, ROESY, extended COSY, and DISCO.
