Transmembrane and water-soluble helix bundles display reverse patterns of surface roughness.

Amino acid exposure and surface roughness were calculated for 12 helices from three transmembrane alpha-helix bundles and 13 helices from seven water-soluble alpha-helix bundles. Transmembrane helix bundles have relatively rough surfaces exposed to the lipid bilayer hydrocarbon chains and relatively smooth surfaces along helix-helix interfaces. This pattern is the reverse of what occurs in water-soluble helix bundles, where relatively rough surfaces are at the helix-helix interfaces and relatively smooth surfaces are exposed to water. The relatively rough exposed surfaces and buried smooth surfaces of transmembrane helices are likely to contribute to the stability of transmembrane helical bundles in a phospholipid environment.