2wud
Crystal structure of S114A mutant of HsaD from Mycobacterium tuberculosis
Structural highlights
FunctionHSAD_MYCTU Catalyzes the hydrolysis of a carbon-carbon bond in 4,5: 9,10-diseco-3-hydroxy-5,9,17-trioxoandrosta-1(10),2-diene-4-oate (4,9-DSHA) to yield 9,17-dioxo-1,2,3,4,10,19-hexanorandrostan-5-oate (DOHNAA) and 2-hydroxy-hexa-2,4-dienoate (HHD). Is also able to catalyze the hydrolysis of 2-hydroxy-6-oxo-6-phenylhexa-2,4-dienoic acid (HOPDA) and the synthetic analog 8-(2-chlorophenyl)-2-hydroxy-5-methyl-6-oxoocta-2,4-dienoic acid (HOPODA).[1] Evolutionary Conservation Check, as determined by ConSurfDB. You may read the explanation of the method and the full data available from ConSurf. Publication Abstract from PubMedIn the recently identified cholesterol catabolic pathway of Mycobacterium tuberculosis, 2-hydroxy-6-oxo-6-phenylhexa-2,4-dienoate hydrolase (HsaD) is proposed to catalyze the hydrolysis of a carbon-carbon bond in 4,5-9,10-diseco-3-hydroxy-5,9,17-tri-oxoandrosta-1(10),2-diene-4-oic acid (DSHA), the cholesterol meta-cleavage product (MCP) and has been implicated in the intracellular survival of the pathogen. Herein, purified HsaD demonstrated 4-33 times higher specificity for DSHA (k(cat)/K(m) = 3.3 +/- 0.3 x 10(4) m(-1) s(-1)) than for the biphenyl MCP 2-hydroxy-6-oxo-6-phenylhexa-2,4-dienoic acid (HOPDA) and the synthetic analogue 8-(2-chlorophenyl)-2-hydroxy-5-methyl-6-oxoocta-2,4-dienoic acid (HOPODA), respectively. The S114A variant of HsaD, in which the active site serine was substituted with alanine, was catalytically impaired and bound DSHA with a K(d) of 51 +/- 2 mum. The S114A.DSHA species absorbed maximally at 456 nm, 60 nm red-shifted versus the DSHA enolate. Crystal structures of the variant in complex with HOPDA, HOPODA, or DSHA to 1.8-1.9 Aindicate that this shift is due to the enzyme-induced strain of the enolate. These data indicate that the catalytic serine catalyzes tautomerization. A second role for this residue is suggested by a solvent molecule whose position in all structures is consistent with its activation by the serine for the nucleophilic attack of the substrate. Finally, the alpha-helical lid covering the active site displayed a ligand-dependent conformational change involving differences in side chain carbon positions of up to 6.7 A, supporting a two-conformation enzymatic mechanism. Overall, these results provide novel insights into the determinants of specificity in a mycobacterial cholesterol-degrading enzyme as well as into the mechanism of MCP hydrolases. Characterization of a carbon-carbon hydrolase from Mycobacterium tuberculosis involved in cholesterol metabolism.,Lack NA, Yam KC, Lowe ED, Horsman GP, Owen RL, Sim E, Eltis LD J Biol Chem. 2010 Jan 1;285(1):434-43. Epub 2009 Oct 29. PMID:19875455[2] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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