Polyphenolic acetates: A newer anti-Mycobacterial therapeutic option

Abstract

The objective of our research project was screening of various highly specific substrates of Acetoxy Drug: Protein Transacytylase (M.TAase) for antimycobacterial activity. Mycobacterial culture was done in Middlebrook’s 7H9 media. Protein purification (Mycobacterial Tranacetylase, M.TAase) was done by ion exchange chromatography and its demonstration was done on SDS- polyacrylamide gel electrophoresis (SDS-PAGE) and western blot. Middlebrook’s 7H9 broth was procured from Becton Dickinson. CM-Sepharose, DEAE-Sepharose and Q-Sephharose were purchased from Amersham Pharmacia. Anti acetyl lysine polyclonal antibody was purchased from Cell Signaling. The Middlebrook 7H9 medium was used for M. smegmatis culture. The media was prepared according to the manufacturer’s instructions. The various Polyphenol acetate compounds were tested for their antimycobacterial activities. Minimal inhibitory concentrations (MIC) were calculated by Alamar blue dye assay method. The GST protein was used as a receptor protein and purified Mycobacterial Glutamine Synthetase (GS) as TAase for acetylation by DAMC. To demonstrate the TAase catalyzed acetylation of GST by DAMC, purified M.TAase (GS) was preincubated with GST and DAMC followed by western blot using anti acetyl lysine antibody, which avidly react with the acetylated proteins. The growth pattern of M. smegmatis was diminished under the influence of various polyphenolic acetates (PA) tested for their anti-mycobacterial activity. DAMC and DAMC-5-carboxylic acid was found to have MIC of 40μg/ml whereas DAMC-6-carboxylic acid was reported to have MIC value of 35μg/ml and for ellagic acid tetra acetate (EATA) it was 60μg/ml. Previous work in our lab has led to discovery of a novel enzyme acetoxy drug: protein transacetylase (TAase), catalyzing transfer of acetyl group from various polyphenolic peracetate (PA) to certain receptor proteins such as cytochromes P-450, NADPH cytochrome reductase, nitric oxide synthase (NOS) has been established in various eukaryotic as well as prokaryotic sources. PA(s) irreversible inhibitors of mammalian CYP linked MFO, possibly due to modification of cytochrome p- 450 by acetylation in a reaction catalysed by M.TAase (GS) utilizing PA(s) as a donor of acetyl groups. Accordingly, it was hypothesized that the CYP51 of mycobacteria involved in the cell wall sterol synthesis could possibly be modified by our PA(s) through the novel unknown action of GS as transacetylase leading to the death of mycobacterial cell by way of acetylation catalyzed by acetoxy drug: protein transacetylase (M.TAase or GS).

Keywords: Transacetylase; Glutamine synthetase; Mycobacterium smegmatis; Polyphenolic acetates; Acetoxy drug: protein transacetylase