Peptides in membranes: helicity and hydrophobicity.

Synthetic model membrane-interactive peptides--both of natural and designed sequence--have become convenient and systematic tools for determination of how the membrane-spanning segments within integral membrane proteins confer protein structure and biology. Conformational studies on these peptides demonstrate that the alpha-helix is the natural choice of conformation for a peptide segment in a membrane, and that a helical conformation will arise "automatically" in a peptide above a threshold hydrophobicity that allows it to associate stably with the membrane. Environmental and sequential contexts thus impart conformational versatility to many of the amino acids, thereby providing a mechanism for producing the diverse structural and functional properties of proteins.