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cytochrome P450 family 17, subfamily A, polypeptide 1 Cytochrome P450 17A1 (CYP17A1 or Cyp17a1), also called cytochrome P450c17, steroid 17-alpha-hydroxylase (EC 1.14.14.19)/17,20 lyase (EC 1.14.14.32), or 17-alpha-hydroxyprogesterone aldolase, catalyzes the conversion of pregnenolone and progesterone to their 17-alpha-hydroxylated products and subsequently to dehydroepiandrosterone (DHEA) and androstenedione. It is a dual enzyme that catalyzes both the 17-alpha-hydroxylation and the 17,20-lyase reactions. Severe mutations on the enzyme cause combined 17-hydroxylase/17,20-lyase deficiency (17OHD); patients with 17OHD synthesize 11-deoxycorticosterone (DOC) which causes hypertension and hypokalemia. Loss of 17,20-lyase activity precludes sex steroid synthesis and leads to sexual infantilism. Included in this group is a second 17A P450 from teleost fish, CYP17A2, that is more efficient in pregnenolone 17-alpha-hydroxylation than CYP17A1, but does not catalyze the lyase reaction. CYP17A1 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. |
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