STABILITY OF SECONDARY STRUCTURAL ELEMENTS IN A SOLVENT-FREE ENVIRONMENT - THE ALPHA-HELIX

The stability of the or helix as an element of secondary structure is examined in the absence of solvation, in the gas phase. Mass-analyzed ion kinetic energy (MIKE) spectrometry was applied to measure intercha rge repulsion and intercharge distance in multiply protonated melittin , a polypeptide known to possess a stable helical structure in a numbe r of different environments. The experimental results, interpreted in combination with molecular mechanics calculations, suggest that triply charged melittin retains its secondary structure in the gas phase, Th e stability if the cu-helical conformation of the polypeptide in the a bsence of solvent molecules reflects the fact that a network of intrin sic helical hydrogen bonds is energetically more favorable than unfold ed conformations. (C) 1997 Wiley-Liss, Inc.