The glycosyltransferase gene encoding the enzyme catalyzing the first step of mycothiol biosynthesis (mshA)

Abstract

Mycothiol is the major thiol present in most actinomycetes and is produced from the pseudodisaccharide 1D-myo-inosityl 2-acetamido-2-deoxy-alpha-D-glucopyranoside (GlcNAc-Ins). A transposon mutant of Mycobacterium smegmatis shown to be GlcNAc-Ins and mycothiol deficient was sequenced to identify a putative glycosyltransferase gene designated mshA. The ortholog in Mycobacterium tuberculosis, Rv0486, was used to complement the mutant phenotype.

FIG. 1.

Structure and biosynthetic pathway for MSH. M. tuberculosis genes encoding MshB (Rv1170; GlcNAc-Ins deacetylase) (14), MshC (Rv2130c; ATP-dependent l-Cys:GlcN-Ins ligase) (18), and MshD (Rv0819; acetyltransferase, mycothiol synthase) (9) have been identified.

FIG. 2.

Alignment of the sequences of MshA from M. smegmatis (MshA-Msmeg) and M. tuberculosis (MshA-Mtub) with the sequences of SpsA from Anaebaena sp. strain PCC7120 (SpsA-Anab) and PimB (Rv0557) from M. tuberculosis (PimB-Mtub). The site of the G32D mutation in M. smegmatis mutant 49 is indicated by an asterisk. See the text for a discussion of specifically designated residues and domains; the numbers are numbers in the M. tuberculosis MshA sequence.