cytochrome P450 family 7, subfamily B, polypeptide 1
Cytochrome P450 7B1 (CYP7B1) is also called 25-hydroxycholesterol 7-alpha-hydroxylase (EC 184.108.40.206) or oxysterol 7-alpha-hydroxylase. It catalyzes the 7alpha-hydroxylation of both steroids and oxysterols, and is thus implicated in the metabolism of neurosteroids and bile acid synthesis, respectively. It participates in the alternative (or acidic) pathway of cholesterol catabolism and bile acid biosynthesis. It also mediates the formation of 7-alpha,25-dihydroxycholesterol (7-alpha,25-OHC) from 25-hydroxycholesterol; 7-alpha,25-OHC acts as a ligand for the G protein-coupled receptor GPR183/EBI2, a chemotactic receptor in lymphoid cells. CYP7B1 belongs to the large cytochrome P450 (P450, CYP) superfamily of heme-containing proteins that catalyze a variety of oxidative reactions of a large number of structurally different endogenous and exogenous compounds in organisms from all major domains of life. CYPs bind their diverse ligands in a buried, hydrophobic active site, which is accessed through a substrate access channel formed by two flexible helices and their connecting loop.