Newton Gerald L, Ko Mary, Ta Philong, Av-Gay Yossef, Fahey Robert C
Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, 92093, USA.
Protein Expr Purif. 2006 Jun;47(2):542-50. doi: 10.1016/j.pep.2006.03.003. Epub 2006 Mar 29.
Mycothiol (MSH, AcCys-GlcN-Ins) is the major low molecular weight thiol in actinomycetes and is essential for growth of Mycobacterium tuberculosis. MshB, the GlcNAc-Ins deacetylase, is a key enzyme in MSH biosynthesis. MshB from M. tuberculosis was cloned, expressed, purified, and its properties characterized. Values of k(cat) and K(m) for MshB were determined for the biological substrate, GlcNAc-Ins, and several other good substrates. The substrate specificity of MshB was compared to that of M. tuberculosis mycothiol S-conjugate amidase (Mca), a homologous enzyme having weak GlcNAc-Ins deacetylase activity. Both enzymes are metalloamidases with overlapping amidase activity toward mycothiol S-conjugates (AcCySR-GlcN-Ins). The Ins residue and hydrophobic R groups enhance the activity with both MshB and Mca, but changes in the acyl group attached to GlcN have opposite effects on the two enzymes.
肌醇硫醇（MSH，乙酰半胱氨酸-葡糖胺-肌醇）是放线菌中主要的低分子量硫醇，对结核分枝杆菌的生长至关重要。MshB，即葡糖胺-肌醇脱乙酰酶，是MSH生物合成中的关键酶。来自结核分枝杆菌的MshB被克隆、表达、纯化并对其性质进行了表征。测定了MshB对生物底物葡糖胺-肌醇以及其他几种良好底物的k(cat)和K(m)值。将MshB的底物特异性与结核分枝杆菌肌醇硫醇S-共轭酰胺酶（Mca）进行了比较，Mca是一种具有弱葡糖胺-肌醇脱乙酰酶活性的同源酶。这两种酶都是金属酰胺酶，对肌醇硫醇S-共轭物（乙酰半胱氨酸-SR-葡糖胺-肌醇）具有重叠的酰胺酶活性。肌醇残基和疏水R基团增强了MshB和Mca的活性，但连接在葡糖胺上的酰基变化对这两种酶有相反的影响。
