The selective, non-covalent, often stoichiometric, interaction of a molecule with one or more specific sites on another molecule. [GOC:ceb, GOC:mah, ISBN:0198506732]
The component of a membrane consisting of the gene products and protein complexes having at least some part of their peptide sequence embedded in the hydrophobic region of the membrane. [GOC:dos, GOC:go_curators]