%0 Journal Article
%@ 0006-3495
%A Holtz, JSW
%A Holtz, JH
%A Chi, Z
%A Asher, SA
%D 1999
%F pittir:17806
%J Biophysical Journal
%N 6
%P 3227 - 3234
%T Ultraviolet Raman examination of the environmental dependence of bombolitin I and bombolitin III secondary structure
%U http://d-scholarship-dev.library.pitt.edu/17806/
%V 76
%X Bombolitin I and III (BI and BIII) are small amphiphilic peptides isolated from bumblebee venom. Although they exist in predominately nonhelical conformations in dilute aqueous solutions, we demonstrate, using UV Raman spectroscopy, that they become predominately α-helical in solution at pH > 10, in high ionic Strength solutions, and in the presence of trifluoroethanol (TFE) and dodecylphosphocholine (DPC) micelles. In this paper, we examine the effects of electrostatic and hydrophobic interactions that control folding of BI and Bill by systematically monitoring their secondary structures as a function of solution conditions. We determine the BI and BIII secondary structure contents by using the quantitative UV Raman methodology of Chi et al. (1998. Biochemistry. 37:2854-2864). Our findings suggest that the α-helix turn in BIII at neutral pH is stabilized by a salt bridge between residues Asp2 and Lys5. This initial α-helical turn results in different BI and Bill α-helical folding mechanisms observed in high pH and high salt concentrations: BIII folds from its single α-helix turn close to its N-terminal, whereas the BI α-helix probably nucleates within the C- terminal half. We also used quasielastic light scattering to demonstrate that the BI and Bill α-helix formation in 0.2 M Ca(CIO4)2 is accompanied by formation of trimers and hexamers, respectively.