Model of the topology of SR-BI. SR-BI is a 509-residue glycoprotein with a large extracellular loop (∼403 residues) anchored to the plasma membrane at both the N- and C-termini by transmembrane domains (∼28 and ∼25 residues) which have short extensions into the cytoplasm (∼8 N-terminal residues and ∼45 C-terminal residues). The approximate locations of the cysteines are shown (“C”). The protein is heavily N-glycosylated, and it is palmitoylated on the cysteines in the C-terminal cytoplasmic and transmembrane domains, Cys462 and Cys470 (murine numbering system). Adapted from ref. 11.