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Journal of Bacteriology, December 2000, p. 6958-6963, Vol. 182, No. 24
0021-9193/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.

N-Acetyl-1-D-myo-Inosityl-2-Amino-2-Deoxy-alpha -D-Glucopyranoside Deacetylase (MshB) Is a Key Enzyme in Mycothiol Biosynthesis

Gerald L. Newton,1 Yossef Av-gay,2 and Robert C. Fahey1,*

Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, California 92093,1 and Department of Medicine, University of British Columbia, Vancouver, British Columbia V5Z 3J5, Canada2

Received 19 June 2000/Accepted 19 September 2000

Mycothiol is a novel thiol produced only by actinomycetes and is the major low-molecular-weight thiol in mycobacteria. Mycothiol was previously shown to be synthesized from 1-D-myo-inosityl-2-amino-2-deoxy-alpha -D-glucopyranoside by ligation with cysteine followed by acetylation. A novel mycothiol-dependent detoxification enzyme, mycothiol conjugate amidase, was recently identified in Mycobacterium smegmatis and shown to have a homolog, Rv1082, in Mycobacterium tuberculosis. In the present study we found that a protein encoded by the M. tuberculosis open reading frame Rv1170, a homolog of Rv1082, possesses weak mycothiol conjugate amidase activity but shows substantial deacetylation activity with 1-D-myo-inosityl-2-acetamido-2-deoxy-alpha -D-glucopyranoside (GlcNAc-Ins), a hypothetical mycothiol biosynthetic precursor. The availability of this protein enabled us to develop an assay for GlcNAc-Ins, which was used to demonstrate that GlcNAc-Ins is present in M. smegmatis at a level about twice that of mycothiol. It was shown that GlcNAc-Ins is absent in mycothiol-deficient mutant strain 49 of M. smegmatis and that this strain can concentrate GlcNAc-Ins from the medium and convert it to mycothiol. This demonstrates that GlcNAc-Ins is a key intermediate in the pathway of mycothiol biosynthesis. Assignment of Rv1170 as the gene coding the deacetylase in the M. tuberculosis genome represents the first identification of a gene of the mycothiol biosynthesis pathway. The presence of a large cellular pool of substrate for this enzyme suggests that it may be important in regulating mycothiol biosynthesis.

* Corresponding author. Mailing address: Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, CA 92093-0506. Phone: (619) 534-2163. FAX: (619) 534-4864. E-mail: rcfahey{at}ucsd.edu.

Journal of Bacteriology, December 2000, p. 6958-6963, Vol. 182, No. 24
0021-9193/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.


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