8cho
From Proteopedia
CRYSTAL STRUCTURE OF DELTA5-3-KETOSTEROID ISOMERASE FROM PSEUDOMONAS TESTOSTERONI
Overview
Bacterial Delta 5-3-ketosteroid isomerase (KSI) from Pseudomonas testosteroni has been intensively studied as a prototype for understanding an enzyme-catalyzed allylic rearrangement involving intramolecular proton transfer. Asp38 serves as a general base to abstract the proton from the steroid C4-H, which is a much stronger base than the carboxyl group of this residue. This unfavorable proton transfer requires 11 kcal/mol of energy which has to be provided by favorable interactions between catalytic residues and substrate in the course of the catalytic reaction. How this energy is provided at the active site of KSI has been a controversial issue, and inevitably the enzyme mechanism is not settled. To resolve these issues, we have determined the crystal structure of this enzyme at 2.3 A resolution. The crystal structure revealed that the active site environment of P. testosteroni KSI is nearly identical to that of Pseudomonas putida KSI, whose structure in complex with a reaction intermediate analogue we have determined recently. Comparison of the two structures clearly indicates that the two KSIs should share the same enzyme mechanism involving the stabilization of the dienolate intermediate by the two direct hydrogen bonds to the dienolate oxyanion, one from Tyr14 OH and the other from Asp99 COOH. Mutational analysis of the two residues and other biochemical data strongly suggest that the hydrogen bond of Tyr14 provides the more significant contribution than that of Asp99 to the requisite 11 kcal/mol of energy for the catalytic power of KSI.
About this Structure
8CHO is a Single protein structure of sequence from Comamonas testosteroni. Full crystallographic information is available from OCA.
Reference
Crystal structure and enzyme mechanism of Delta 5-3-ketosteroid isomerase from Pseudomonas testosteroni., Cho HS, Choi G, Choi KY, Oh BH, Biochemistry. 1998 Jun 9;37(23):8325-30. PMID:9622484 Page seeded by OCA on Sun May 4 22:48:55 2008
