FIG 5.

Three different mechanisms for polysaccharide export across the OM. Left schematic, in classical Wzx/Wzy- and ABC transporter-dependent pathways, polysaccharide transfer across the periplasm and OM is mediated by a complex composed of a PCP and an OPX protein with an α-helical barrel in the OM. Middle schematic, in pathways in which the OPX protein lacks domain D4 (^D1D2OPX or ^D1D2D2OPX proteins), a β-barrel protein constitutes the OM part of the composite OPX/β-barrel protein translocon. The D1 to D4 and D1 to D2 rings of the OPX proteins are indicated. In Wzx/Wzy-dependent pathways, the PCP can be associated with a cytoplasmic BY kinase (light orange). Synthesis, polymerization, and translocation of the polysaccharide across the IM are not shown. Right schematic, in synthase-dependent pathways, transfer across the periplasm and the OM depends on a TPR domain-containing protein and a β-barrel protein translocon in the OM.