Three-dimensional model and molecular mechanism of Mycobacterium tuberculosis catalase-peroxidase (KatG) and isoniazid-resistant KatG mutants

• Published in: Microbial drug resistance (Larchmont, N.Y.) Vol. 10; no. 4; p. 269
• Main Authors: Mo, L, Zhang, W, Wang, J, Weng, X H, Chen, S, Shao, L Y, Pang, M Y, Chen, Z W
• Format: Journal Article
• Language: English
• Published: United States 2004
• Subjects: Amino Acid Sequence; Amino Acid Substitution - genetics; Bacterial Proteins - chemistry; Bacterial Proteins - genetics; Catalase - chemistry; Catalase - genetics; Drug Resistance, Bacterial - genetics; Isoniazid - pharmacology; Models, Molecular; Molecular Sequence Data; Mutation; Mycobacterium tuberculosis - enzymology; Oxidation-Reduction; Protein Conformation
• ISSN: 1076-6294
• DOI: 10.1089/mdr.2004.10.269

Mycobacterium tuberculosis KatG enzyme functions both as catalase for removing hydrogen peroxide (H(2)O(2)) and as peroxidase for oxidating isoniazid (INH) to active form of anti-tuberculosis drug. Although mutations in M. tuberculosis KatG confer INH resistance in tuberculous patients, structural bases for INH-resistant mutations in the KatG gene remains poorly understood. Here, three M. tuberculosis KatG mutants bearing Arg418--> Gln, Ser315 --> Thr, or Trp321 --> Gly replacement were assessed for changes in catalase-peroxidase activities and possible structure bases relevant to such changes. These three M. tuberculosis KatG mutants exhibited a marked impairment or loss of catalase-peroxidase activities. The possible structural bases for the mutant-induced loss of enzyme activities were then analyzed using a three-dimensional model of M. tuberculosis KatG protein constructed on the basis of the crystal structure of the catalase-peroxidase from Burkholderia pseudomallei. The model suggests that three M. tuberculosis KatG mutants bearing Arg418 --> Gln, Ser315 -->Thr, or Trp321--> Gly replacement affect enzyme activities by different mechanisms, although each of them impacts consequently on a heme-associated structure, the putative oxidative site. Moreover, in addition to the widely accepted substrate-binding site, M. tuberculosis KatG may bear another H(2)O(2) binding site. This H(2)O(2) binding site appears to interact with the catalytic site by a possible electron-transfer chain, a Met255-Tyr229-Trp107 triad conserved in many catalase-peroxidases. The Ser315 --> Thr mutant may have direct effect on the catalytic site by interfering with electron transfer in addition to the previously proposed mechanism of steric constraint.