How proteins adapt to a membrane–water interface

Membrane proteins present a hydrophobic surface to the surrounding lipid, whereas portions protruding into the aqueous milieu expose a polar surface. But how have proteins evolved to deal with the complex environment at the membrane–water interface? Some insights have been provided by high-resolution structures of membrane proteins, and recent studies of the role of individual amino acids in mediating protein–lipid contacts have shed further light on this issue. It now appears clear that the polar-aromatic residues Trp and Tyr have a specific affinity for a region near the lipid carbonyls, whereas positively charged residues extend into the lipid phosphate region.