Topology and identification of critical residues of the O-acetyltransferase of serotype-converting bacteriophage, SF6, of Shigella flexneri

The modification of the LPS O-antigen, seen in the diverse serotypes of Shigella flexneri is brought about by the glucosyltransferases (Gtr) and the O-acetyltransferase (Oac). In this study, we establish the membrane topology of Oac using the dual reporter PhoA–LacZα. We have determined that Oac is an integral membrane protein with 10 transmembrane regions. The hydrophilic N- and C-termini are oriented in the cytoplasm. Functionally important cytoplasmic and periplasmic loops have also been identified. Furthermore, cytoplasmic residues R73 and R75R76 were found to be critical to Oac function.