Figure 1.

Synthase- and Wzx/Wzy-dependent secretion systems in Gram-negative bacteria. (A) In the synthase-dependent pathway, sugars are polymerized and translocated across the IM by a GT (salmon) in response to c-di-GMP binding a c-di-GMP receptor protein (pink). Once in the periplasm, the sugar polymer can be modified by periplasmic modifying enzymes (periwinkle). Transport across the OM is facilitated by a ß-barrel protein (yellow) and TPR-containing protein (green). (B) The Wzx/Wzy-dependent pathway, a sugar polymer repeat unit is assembled on a undecaprenyl-phosphate lipid carrier by GTs. A Wzx flippase (bright green) translocates the repeat unit across the IM where a Wzy glycosyltransferase (dark blue) assembles repeat units to form the polymer. The polymer is transported across the periplasm and OM by a PCP protein and an OPX protein. IM, inner membrane; PG, peptidoglycan; OM, outer membrane; NDP, nucleotide disphosphate; NMP, nucleotide monophosphate; and Phos, phosphate molecule.