Characterizing properties of bacterial outer membrane polysaccharide export (OPX) proteins

Abstract

Many pathogenic bacteria produce capsules; virulence factors that hinder clearance by mammalian immune systems. Capsular polysaccharide (CPS) biosynthesis and export pathways of Gram-negative bacteria are classified by their assembly system; group 1 or 2 in Escherichia coli, which employ outer membrane polysaccharide export (OPX) proteins to translocate CPS to the cell surface. The only structurally characterized OPX protein is Wza from E. coli K30 (group 1). This research focused on characterization of OPX proteins from group 2 systems in E. coli K1 (KpsD) and Salmonella enterica serovar Typhi (VexA) with comparisons to Wza. All three OPX proteins localized to the outer membrane. KpsD behaved like a peripheral membrane protein and large amounts were found in the periplasm. Wza and VexA are lipoproteins and associated with LolA, a chaperone in the lipoprotein export pathway. These studies indicate different properties in OPX proteins are not exclusive to a particular pathway.