Novel mutations in <Emphasis Type="Italic">katG</Emphasis> gene of a clinical isolate of isoniazid-resistant <Emphasis Type="Italic">Mycobacterium tuberculosis</Emphasis>

Most of isoniazid-resistant Mycobacterium tuberculosis evolved due to mutation in the katG gene encoding catalase-peroxidase. A set of new mutations, namely T1310C, G1388T, G1481A, T1553C, and A1660G, which correspond to amino acid substitutions of L437P, R463L, G494D, I518T, and K554E, in the katG gene of the L10 clinical isolate M. tuberculosis was identified. The wild-type and mutant KatG proteins were expressed in Escherichia coli BL21(DE3) as a protein of 80 kDa based on sodium dodecyl sulphate-polyacrylamide gel electrophoresis analysis. The mutant KatG protein exhibited catalase and peroxidase activities of 4.6% and 24.8% toward its wild type, respectively, and retained 19.4% isoniazid oxidation activity. The structure modelling study revealed that these C-terminal mutations might have induced formation of a new turn, perturbing the active site environment and also generated new intramolecular interactions, which could be unfavourable for the enzyme activities.     

Biochemical characterization of a glucoamylase from Saccharomycopsis fibuligera R64

Glucoamylase from the yeast Saccharomycopsis fibuligera R64 (GLL1) has successfully been purified and characterized. The molecular mass of the enzyme was 56,583 Da as determined by mass spectrometry. The purified enzyme demonstrated optimum activity in the pH range of 5.6–6.4 and at 50°C. The activity of the enzyme was inhibited by acarbose with the IC₅₀ value of 5 μM. GLL1 shares high amino acid sequence identity with GLU1 and GLA1, which are Saccharomycopsis fibuligera glucoamylases from the strains HUT7212 and KZ, respectively. The properties of GLL1, however, resemble that of GLU1. The elucidation of the primary structure of GLL1 contributes to the explanation of this finding.