1QJG
Crystal structure of delta5-3-ketosteroid isomerase from Pseudomonas testosteroni in complex with equilenin
Summary for 1QJG
| Entry DOI | 10.2210/pdb1qjg/pdb |
| Related | 1ISK 8CHO |
| Descriptor | KETOSTEROID ISOMERASE, EQUILENIN, SULFATE ION, ... (4 entities in total) |
| Functional Keywords | ketosteroid isomerase, ksi, isomerase, steroid isomeration |
| Biological source | PSEUDOMONAS TESTOSTERONI |
| Total number of polymer chains | 6 |
| Total formula weight | 82233.09 |
| Authors | Cho, H.-S.,Oh, B.-H. (deposition date: 1999-06-24, release date: 1999-11-16, Last modification date: 2023-12-13) |
| Primary citation | Cho, H.-S.,Ha, N.-C.,Choi, G.,Kim, H.-J.,Lee, D.,Oh, K.S.,Kim, K.S.,Lee, W.,Choi, K.Y.,Oh, B.-H. Crystal Structure of Delta-5-3-Ketosteroid Isomerase from Pseudomonas Testosteroni in Complex with Equilenin Settles the Correct Hydrogen Scheme for Transition-State Stabilization J.Biol.Chem., 274:32863-, 1999 Cited by PubMed Abstract: Delta(5)-3-Ketosteroid isomerase from Pseudomonas testosteroni has been intensively studied as a prototype to understand an enzyme-catalyzed allylic isomerization. Asp(38) (pK(a) approximately 4.7) was identified as the general base abstracting the steroid C4beta proton (pK(a) approximately 12.7) to form a dienolate intermediate. A key and common enigmatic issue involved in the proton abstraction is the question of how the energy required for the unfavorable proton transfer can be provided at the active site of the enzyme and/or how the thermodynamic barrier can be drastically reduced. Answering this question has been hindered by the existence of two differently proposed enzyme reaction mechanisms. The 2.26 A crystal structure of the enzyme in complex with a reaction intermediate analogue equilenin reveals clearly that both the Tyr(14) OH and Asp(99) COOH provide direct hydrogen bonds to the oxyanion of equilenin. The result negates the catalytic dyad mechanism in which Asp(99) donates the hydrogen bond to Tyr(14), which in turn is hydrogen bonded to the steroid. A theoretical calculation also favors the doubly hydrogen-bonded system over the dyad system. Proton nuclear magnetic resonance analyses of several mutant enzymes indicate that the Tyr(14) OH forms a low barrier hydrogen bond with the dienolic oxyanion of the intermediate. PubMed: 10551849DOI: 10.1074/JBC.274.46.32863 PDB entries with the same primary citation |
| Experimental method | X-RAY DIFFRACTION (2.3 Å) |
Structure validation
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