The internalization of various cargo proteins and lipids from the mammalian cell surface
occurs through the clathrin and lipid-raft endocytic pathways. Protein–lipid and protein–
protein interactions control the targeting of signalling molecules and their partners to various
specialized membrane compartments in these pathways. This functions to control the activity
of signalling cascades and the termination of signalling events, and therefore has a key role
in defining how a cell responds to its environment.