Sequence and function of the aas gene in Escherichia coli

Abstract

2-Acylglycerophosphoethanolamine (2-acyl-GPE) acyltransferase and acyl-acyl carrier protein (acyl-ACP) synthase activities are encoded by the aas gene in Escherichia coli. The aas gene was cloned, and the DNA sequence of the aas gene and the region between aas and galR established the clockwise gene order in the 61.2 min of the E. coli chromosome as aas-orf-galR-lysA-lysR-orf-araE. The aas gene consists of a single open reading frame of 2,157 base pairs predicted to encode a protein of 80.6 kDa. Strains harboring multiple copies of the aas gene overproduced both 2-acyl-GPE acyltransferase and acyl-ACP synthetase activities in vitro and had higher specific activities for the incorporation of exogenous fatty acids and lysophospholipids into the membrane in vivo. Specific expression of the aas gene yielded a protein with an apparent molecular mass of 81 kDa. Comparison of the predicted amino acid sequence of the aas gene with mammalian, yeast, and bacterial long chain acyl-coenzyme A synthetases revealed three domains of high similarity which are postulated to form the acyl-AMP binding pocket. These data verify that 2-acyl-GPE acyltransferase and acyl-ACP synthetase are reactions carried out by the same gene product, verify the role of 2-acyl-GPE acyltransferase/acyl-ACP synthetase in the acylation of endogenous 2-acyl-GPE, and establish the product of the aas gene as the rate-limiting enzyme in the uptake and incorporation of exogenous 2-acyllysophospholipids.