FIG 7 .

Model of rhamnan biosynthesis in L. lactis. The rhamnan chain is assembled on a lipid carrier (undecaprenylphosphate) in the bacterial cytoplasm. Proteins RmlA to RmlD synthesize dTDP-l-Rha precursor. TagO is the initial transferase catalyzing the transfer of GlcNAc onto undecaprenylphosphate. RgpA adds a first l-Rha, and then RgpB and RgpF are involved in the processive elongation of the chain, catalyzing the transfer of l-Rha into positions 3 and 2, respectively, of the previous l-Rha. A putative terminal sugar (GlcNAc or Glc, added by an unknown enzyme) terminates the synthesis of the chain. An ABC transporter exports the rhamnan from the cytoplasm to the extracellular side of the cytoplasmic membrane. Finally, phosphorhamnan chains are transferred onto peptidoglycan chains by LCP protein(s), with LcpA playing the main role.