Substrate recognition and catalytic mechanism of the phosphate acyltransferase PlsX from Bacillus subtilis.

Phosphate: acyl-acyl carrier protein (ACP) acyltransferase PlsX is a peripheral enzyme catalyzing acyl transfer to orthophosphate in phospholipid synthesis. Little is known about how it recognizes substrates and catalyzes the acyl transfer reaction. Here we show that its active site include many residues lining a long narrow gorge at the dimeric interface, two positive residues forming a positive ACP docking pad next to the interfacial gorge, and a number of strictly conserved residues significantly contributing to the catalytic activity. These findings suggest a substrate recognition mode and a catalytic mechanism that is different from phosphotransacetylases catalyzing a similar acyl transfer reaction. The catalytic mechanism involves substrate activation and transition state stabilization by two strictly conserved residues, lysine-184 and asparagine-229. Another noticeable feature of the catalysis is the release of the acyl phosphate product to membrane proximity which may facilitate its membrane insertion.