Fig. 1.—

Residue environments within membrane proteins. A cartoon diagram of a membrane protein in cross section. Residues from membrane proteins fall into two distinct types of regions: TM regions (red), which lie within the membrane in which the protein is embedded, and EM regions (blue), which lie outside of the membrane. In both TM and EM regions, residues experience different degrees of burial within the protein, ranging from completely buried to highly exposed.