The last step in the biosynthesis of dithiolopyrrolone antibiotics was thought to involve the transfer of acyl group from acyl-CoA to pyrrothine/holothin core. In Saccharothrix algeriensis NRRL B-24137, two acyltransferases, an acetyltransferase and a benzoyltransferase were proposed to catalyze this step. We have previously identified, in Sa. algeriensis genome, two open read frames, actA and actB patiently encoded these enzymes. This study focuses primarily on the characterization of the protein encoded by actA. After cloning and expressing of actA in Escherichia coli BL21, the recombinant protein encoded by actA was purified. Selectivity of ActA for pyrrothine/holothin as substrate and different acyl-CoA as co-substrate was evaluated using two acyls-groups, linear and aromatic. The enzyme was shown to prefer aromatic groups over linear groups as donor group; further neither product nor transfer was observed for linear groups. Therefore ActA has been determined to be a pyrrothine/holothin N-benzoyltransferase which can either pyrrothine (Km of 72μM) or holothin (Km of 129.5μM) as substrates and benzoyl-CoA (Km of 348.65 and 395.28μM) as co-substrates for pyrrothine and holothin, respectively. The optimum pH and temperature has been shown to be 8, 40°C, respectively. ActA is the first enzyme characterized as N-benzoyltransferase in bacteria.
Keywords: Benzoyl-holothin; Benzoyl-pyrrothine; Holothin; N-benzoyltransferase; Pyrrothine; Saccharothrix algeriensis.
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