The Ssc protein of enteric bacteria has significant homology to the acyltransferase Lpxa of lipid A biosynthesis, and to three acetyltransferases

Abstract

The Sse protein, a novel essential protein affecting the function of the enterobacteriai outer membrane, matched in a protein homology search best with LpxA (UDP-N-aeetylglucosamine 3-hydroxymyristoyl transferase), the enzyme which eata!yzes the first step of lipid A biosynthesis. The corresponding genes, located 0.56 kb apart, were 46.7% identical. The search also revealed homology to the bacterial acetyltransferzee_~ LaeA and NodL, as well as to a hypothetical protein Yglm. The region of residues 109-149 Sse displayed the highest homology and was also homologous with another bacterial acetyltransferase, CysE, and three other bacterial proteins, two of which are hypothetical. This region and the corresponding regions of all other proteins were found to have a peculiar repeated hexapeptide pattern. Each hexapeptide unit starts with isoleucine (or its equivalent leucine and valine). In most units, the second residue is glyeine and the fifth residue either valine or alanine.