TABLE 1.

Pathways and receptors involved in cholesterol efflux from cells to HDL and apoA-I

Efflux pathway	Energetics	Receptor characteristics
		Number of amino acids/monomera	Number of transmembrane helices/monomer	State of self-association
Aqueous diffusion	Passive
Scavenger receptor class B, type I (SR-BI)	Passive	552	2	Homodimer
ATP-binding cassette transporter G1 (ABCG1)	Active	678	6	Homodimer
ATP-binding cassette transporter A1 (ABCA1)	Active	2261	12	Dimer/tetramer

^a Data for the human proteins were taken from the Swiss-Prot UniProt database. SR-BI and ABCG1 exhibit polymorphism.