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Title: Structure and Mechanism of MbtI, the Salicylate Synthase from Mycobacterium tuberculosis

Abstract

MbtI (rv2386c) from Mycobacterium tuberculosis catalyzes the initial transformation in mycobactin biosynthesis by converting chorismate to salicylate. We report here the structure of MbtI at 2.5 {angstrom} resolution and demonstrate that isochorismate is a kinetically competent intermediate in the synthesis of salicylate from chorismate. At pH values below 7.5 isochorismate is the dominant product while above this pH value the enzyme converts chorismate to salicylate without the accumulation of isochorismate in solution. The salicylate and isochorismate synthase activities of MbtI are Mg{sup 2+}-dependent, and in the absence of Mg{sup 2+} MbtI has a promiscuous chorismate mutase activity similar to that of the isochorismate pyruvate lyase, PchB, from Pseudomonas aeruginosa. MbtI is part of a larger family of chorismate-binding enzymes descended from a common ancestor (the MST family), that includes the isochorismate synthases and anthranilate synthases. The lack of active site residues unique to pyruvate eliminating members of this family, combined with the observed chorismate mutase activity, suggests that MbtI may exploit a sigmatropic pyruvate elimination mechanism similar to that proposed for PchB. Using a combination of structural, kinetic, and sequence based studies we propose a mechanism for MbtI applicable to all members of the MST enzyme family.

Authors:
; ; ; ;
Publication Date:
Research Org.:
Brookhaven National Laboratory (BNL) National Synchrotron Light Source
Sponsoring Org.:
Doe - Office Of Science
OSTI Identifier:
930309
Report Number(s):
BNL-81019-2008-JA
Journal ID: ISSN 0006-2960; TRN: US200822%%1252
DOE Contract Number:  
DE-AC02-98CH10886
Resource Type:
Journal Article
Resource Relation:
Journal Name: Biochemistry; Journal Volume: 46
Country of Publication:
United States
Language:
English
Subject:
59 BASIC BIOLOGICAL SCIENCES; ENZYMES; MYCOBACTERIUM TUBERCULOSIS; SYNTHESIS; SALICYLIC ACID; CARBOXYLIC ACID SALTS; CATALYTIC EFFECTS; MORPHOLOGY; national synchrotron light source

Citation Formats

Zwahlen,J., Kolappan, S., Zhou, R., Kisker, C., and Tonge, P. Structure and Mechanism of MbtI, the Salicylate Synthase from Mycobacterium tuberculosis. United States: N. p., 2007. Web. doi:10.1021/bi060852x.
Zwahlen,J., Kolappan, S., Zhou, R., Kisker, C., & Tonge, P. Structure and Mechanism of MbtI, the Salicylate Synthase from Mycobacterium tuberculosis. United States. doi:10.1021/bi060852x.
Zwahlen,J., Kolappan, S., Zhou, R., Kisker, C., and Tonge, P. Mon . "Structure and Mechanism of MbtI, the Salicylate Synthase from Mycobacterium tuberculosis". United States. doi:10.1021/bi060852x.
@article{osti_930309,
title = {Structure and Mechanism of MbtI, the Salicylate Synthase from Mycobacterium tuberculosis},
author = {Zwahlen,J. and Kolappan, S. and Zhou, R. and Kisker, C. and Tonge, P.},
abstractNote = {MbtI (rv2386c) from Mycobacterium tuberculosis catalyzes the initial transformation in mycobactin biosynthesis by converting chorismate to salicylate. We report here the structure of MbtI at 2.5 {angstrom} resolution and demonstrate that isochorismate is a kinetically competent intermediate in the synthesis of salicylate from chorismate. At pH values below 7.5 isochorismate is the dominant product while above this pH value the enzyme converts chorismate to salicylate without the accumulation of isochorismate in solution. The salicylate and isochorismate synthase activities of MbtI are Mg{sup 2+}-dependent, and in the absence of Mg{sup 2+} MbtI has a promiscuous chorismate mutase activity similar to that of the isochorismate pyruvate lyase, PchB, from Pseudomonas aeruginosa. MbtI is part of a larger family of chorismate-binding enzymes descended from a common ancestor (the MST family), that includes the isochorismate synthases and anthranilate synthases. The lack of active site residues unique to pyruvate eliminating members of this family, combined with the observed chorismate mutase activity, suggests that MbtI may exploit a sigmatropic pyruvate elimination mechanism similar to that proposed for PchB. Using a combination of structural, kinetic, and sequence based studies we propose a mechanism for MbtI applicable to all members of the MST enzyme family.},
doi = {10.1021/bi060852x},
journal = {Biochemistry},
number = ,
volume = 46,
place = {United States},
year = {Mon Jan 01 00:00:00 EST 2007},
month = {Mon Jan 01 00:00:00 EST 2007}
}