Solubilization of V-ATPase transmembrane peptides by amphipol A8-35

Two transmembrane peptides encompassing the seventh transmembrane section of subunit a from V-ATPase from Saccharomyces cerevisiae were studied as complexes with APols A8-35 by CD and fluorescence spectroscopy, with the goal to use APols to provide a membrane-mimicking environment for the peptides. CD spectroscopy was used to obtain the overall secondary structure of the peptides, whereas fluorescence spectroscopy provided information about the local environment of their tryptophan residues. The fluorescence results indicate that both peptides are trapped by APols and the CD results that they adopt a beta-sheet conformation. This result is in contrast with previous work that showed that the same peptides are alpha-helical in SDS micelles and organic solvents. These observations are discussed in the context of APol physical-chemical properties and transmembrane peptide structural propensity.