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Crystal structure of the HsaA monooxygenase from M. tuberculosisCrystal structure of the HsaA monooxygenase from M. tuberculosis
Structural highlights
FunctionHSAA_MYCTU Catalyzes the o-hydroxylation of 3-hydroxy-9,10-secoandrosta-1,3,5(10)-triene-9,17-dione (3-HSA) to 3,4-dihydroxy-9,10-secoandrosta-1,3,5(10)-triene-9,17-dione (3,4-DHSA) in the catabolism of cholesterol. Can use either FADH(2) or FMNH(2) as flavin cosubstrate. Also catalyzes the o-hydroxylation of a range of p-substituted phenols to generate the corresponding catechols.[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 PubMedMycobacterium tuberculosis (Mtb) and Rhodococcus jostii RHA1 have similar cholesterol catabolic pathways. This pathway contributes to the pathogenicity of Mtb. The hsaAB cholesterol catabolic genes have been predicted to encode the oxygenase and reductase, respectively, of a flavin-dependent mono-oxygenase that hydroxylates 3-hydroxy-9,10-seconandrost-1,3,5(10)-triene-9,17-dione (3-HSA) to a catechol. An hsaA deletion mutant of RHA1 did not grow on cholesterol but transformed the latter to 3-HSA and related metabolites in which each of the two keto groups was reduced: 3,9-dihydroxy-9,10-seconandrost-1,3,5(10)-triene-17-one (3,9-DHSA) and 3,17-dihydroxy-9,10-seconandrost-1,3,5(10)-triene-9-one (3,17-DHSA). Purified 3-hydroxy-9,10-seconandrost-1,3,5(10)-triene-9,17-dione 4-hydroxylase (HsaAB) from Mtb had higher specificity for 3-HSA than for 3,17-DHSA (apparent k(cat)/K(m) = 1000 +/- 100 M(-1) s(-1) versus 700 +/- 100 M(-1) s(-1)). However, 3,9-DHSA was a poorer substrate than 3-hydroxybiphenyl (apparent k(cat)/K(m) = 80 +/- 40 M(-1) s(-1)). In the presence of 3-HSA the K(m)(app) for O(2) was 100 +/- 10 microM. The crystal structure of HsaA to 2.5-A resolution revealed that the enzyme has the same fold, flavin-binding site, and catalytic residues as p-hydroxyphenyl acetate hydroxylase. However, HsaA has a much larger phenol-binding site, consistent with the enzyme's substrate specificity. In addition, a second crystal form of HsaA revealed that a C-terminal flap (Val(367)-Val(394)) could adopt two conformations differing by a rigid body rotation of 25 degrees around Arg(366). This rotation appears to gate the likely flavin entrance to the active site. In docking studies with 3-HSA and flavin, the closed conformation provided a rationale for the enzyme's substrate specificity. Overall, the structural and functional data establish the physiological role of HsaAB and provide a basis to further investigate an important class of monooxygenases as well as the bacterial catabolism of steroids. A flavin-dependent monooxygenase from Mycobacterium tuberculosis involved in cholesterol catabolism.,Dresen C, Lin LY, D'Angelo I, Tocheva EI, Strynadka N, Eltis LD J Biol Chem. 2010 Jul 16;285(29):22264-75. Epub 2010 May 6. PMID:20448045[2] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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