Synthetic putative transmembrane region of minimal potassium channel protein (minK) adopts an α-helical conformation in phospholipid membranes

Abstract

Minimal potassium channel protein (minK) is a potassium channel protein consisting of 130 amino acids, possessing just one putative transmembrane domain. In this study we have synthesized a peptide with the amino acid sequence RDDSKLEALYILMVLGFFGFFTLGIMLSYI, containing the putative transmembrane region of minK, and analysed its secondary structure by using Fourier-transform IR and CD spectroscopy. The peptide was virtually insoluble in aqueous buffer, forming intermolecular β-sheet aggregates. On attempted incorporation of the peptide into phospholipid membranes with a method involving dialysis, the peptide adopted a predominantly intermolecular β-sheet conformation identical with that of the peptide in aqueous buffer, in agreement with a previous report. However, by using an alternative method of incorporating the peptide into phospholipid membranes we found that the peptide adopted a predominantly α-helical conformation, a finding consistent with various proposed structural models. These observed differences in secondary structure are due to artifacts of aggregation of the peptide before incorporation into lipid.