CONFORMATIONAL STUDY OF SEQUENTIAL LYS-BASED AND LEU-BASED POLYMERS AND OLIGOMERS USING VIBRATIONAL AND ELECTRONIC CD-SPECTRA

Vibrational CD (VCD) and electronic CD (ECD) spectra of some sequentia l Lys and Leu based oligo- and polypeptides were studied as a function of added salt and (for ECD) as a function of concentration in aqueous solution. For these samples, the VCD spectra can only be measured at relatively high concentrations under which the well-known salt-induced transition to a beta-sheet form can be observed for the KL based spec ies, but only the end-state alpha-helical conformation is obvious for the LKKL based samples. ECD concentration dependence demonstrates that , at high concentration with no added or with added salt, LKKL based o ligomers and polymers give alpha-helical spectra. These data provide e vidence of aggregation induced secondary structure formation in an exc eptionally simple peptide system. Similarly, the KL based oligomers an d polymers give beta-sheet like spectra at high concentration or at hi gh salt. These systems further provide model systems under ''normal'' aqueous conditions that yield VCD band shapes that correlate to the ma jor secondary structural types of polypeptides. They are in substantia l agreement with those spectra obtained on homopolypeptides and on pro teins, confirming the relative independence of the VCD technique from side-chain and solvent effects. (C) 1994 John Wiley & Sons, Inc.