1buq
From Proteopedia
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SOLUTION STRUCTURE OF DELTA-5-3-KETOSTEROID ISOMERASE COMPLEXED WITH THE STEROID 19-NORTESTOSTERONE-HEMISUCCINATE
Overview
The solution structure of the ketosteroid isomerase homodimer complexed, with the product analogue 19-nortestosterone hemisuccinate (19-NTHS) was, solved by heteronuclear multidimensional NMR methods using 1647 distance, restraints, 77 dihedral angle (phi) restraints, and 67 hydrogen bond, restraints per monomer. The refined secondary structure of each subunit, consists of three alpha-helices, eight beta-strands, four turns, and two, beta-bulges. The beta-strands form a mixed beta-sheet. One of the five, proline residues, Pro-39, is cis and begins a nonclassical turn. A, self-consistent ensemble of 15 tertiary/quaternary structures of the, enzyme dimer-steroid complex, with no distance violations greater than, 0.35 A, was generated by simulated annealing and energy minimization with, the program X-PLOR. The mean pairwise RMSD of the secondary structural, elements was 0.63 A for the average subunit and 1.25 A for the dimer., Within each subunit, the three alpha-helices are packed onto the concave, surface of the beta-sheet with a groove between them into which the, steroid binds at a site defined by 14 intermolecular distances. In the, productive complex, Tyr-14, from alpha-helix 1, approaches both Asp-99 and, the 3-keto group of 19-NTHS while, from beta-strand 1, the carboxylate of, Asp-38 approaches the beta-face of the steroid near C4 and C6, between, which it transfers a proton during catalysis. Thus the solution structure, of the isomerase-steroid complex can accommodate the catalytic diad, mechanism in which Asp-99 donates a hydrogen bond to Tyr-14 which in turn, is hydrogen bonded to the 3-oxygen of the steroid. While direct hydrogen, bonding of Asp-99 to the steroid oxygen is less likely, it cannot be, excluded. All other interactions of the steroid with the enzyme are, hydrophobic. The dimer interface, which is between the convex surfaces of, the beta-sheets, is defined by 28 intersubunit NOEs between hydrophobic, residues in the 13C-filtered NOESY-HSQC spectrum of a, 13C/12C-heterolabeled dimer. Both hydrophobic and polar interactions occur, at the dimer interface which contains no space that would permit, additional steroid binding. Comparison of the complexed enzyme with the, solution structure of the free enzyme [Wu et al. (1997) Science 276, 415-418] reveals that the three helices change position in the steroid, complex, becoming more closely packed onto the concave surface of the, beta-sheet, thus bringing Tyr-14 closer to Asp-99 and the substrate., Comparison of the enzyme-steroid complex in solution with the free enzyme, in the crystalline state reveals similar differences between the positions, of the helices.
About this Structure
1BUQ is a Single protein structure of sequence from Comamonas testosteroni with NTH as ligand. Active as Steroid Delta-isomerase, with EC number 5.3.3.1 Full crystallographic information is available from OCA.
Reference
Solution structure of Delta 5-3-ketosteroid isomerase complexed with the steroid 19-nortestosterone hemisuccinate., Massiah MA, Abeygunawardana C, Gittis AG, Mildvan AS, Biochemistry. 1998 Oct 20;37(42):14701-12. PMID:9778345
Page seeded by OCA on Tue Nov 20 11:56:22 2007
