Structural highlights
FunctionPublication Abstract from PubMed3-Ketosteroid Delta4-(5alpha)-dehydrogenases (Delta4-(5alpha)-KSTDs) are enzymes that introduce a double bond between the C4 and C5 atoms of 3-keto-(5alpha)-steroids. Here we show that the ro05698 gene from Rhodococcus jostii RHA1 codes for a flavoprotein with Delta4-(5alpha)-KSTD activity. The 1.6 A resolution crystal structure of the enzyme revealed three conserved residues (Tyr-319, Tyr-466, and Ser-468) in a pocket near the isoalloxazine ring system of the FAD co-factor. Site-directed mutagenesis of these residues confirmed that they are absolutely essential for catalytic activity. A crystal structure with bound product 4-androstene-3,17-dione showed that Ser-468 is in a position in which it can serve as the base abstracting the 4beta-proton from the C4 atom of the substrate. Ser-468 is assisted by Tyr-319, which possibly is involved in shuttling the proton to the solvent. Tyr-466 is at hydrogen bonding distance to the C3 oxygen atom of the substrate and can stabilize the keto-enol intermediate occurring during the reaction. Finally, the FAD N5 atom is in a position to be able to abstract the 5alpha-hydrogen of the substrate as a hydride ion. These features fully explain the reaction catalyzed by Delta4-(5alpha)-KSTDs. Structure and Catalytic Mechanism of 3-Ketosteroid-{Delta}4-(5alpha)-dehydrogenase from Rhodococcus jostii RHA1 Genome.,van Oosterwijk N, Knol J, Dijkhuizen L, van der Geize R, Dijkstra BW J Biol Chem. 2012 Sep 7;287(37):30975-83. Epub 2012 Jul 24. PMID:22833669[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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