SYNTHETIC PUTATIVE TRANSMEMBRANE REGION OF MINIMAL POTASSIUM CHANNEL PROTEIN (MINK) ADOPTS AN ALPHA-HELICAL CONFORMATION IN PHOSPHOLIPID-MEMBRANES

Minimal potassium channel protein (minK) is a potassium channel protei n consisting of 130 amino acids, possessing just one putative transmem brane domain. In this study we have synthesized a peptide with the ami no acid sequence RDDSKLEALYILMVLGFFGFFTLGIMLSYI, containing the putati ve transmembrane region of minK, and analysed its secondary structure by using Fourier-transform IR and CD spectroscopy. The peptide was vir tually insoluble in aqueous buffer, forming intermolecular P-sheet agg regates. On attempted incorporation of the peptide into phospholipid m embranes with a method involving dialysis, the peptide adopted a predo minantly intermolecular P-sheet conformation identical with that of th e peptide in aqueous buffer, in agreement with a previous report [Horv ath, Heimburg, Kovachev, Findlay, Hideg and Marsh, (1995) Biochemistry 34, 3893-3898]. However, by using an alternative method of incorporat ing the peptide into phospholipid membranes we found that the peptide adopted a predominantly cc-helical conformation, a finding consistent with various proposed structural models. These observed differences in secondary structure are due to artifacts of aggregation of the peptid e before incorporation into lipid.