1.B.73 The Capsule Biogenesis/Assembly (CBA) Family
Many pathogenic bacteria encase themselves in a polysaccharide capsule that provides a barrier to the physical and immunological challenges of the host. The mechanism by which the capsule assembles around the bacterial cell is poorly understood. Wzi, an integral outer-membrane protein from E. coli, has been implicated in the formation of group 1 capsules (Rahn et al. 2003). The 2.6 Å resolution structure of Wzi revealed an 18-stranded β-barrel fold with a novel arrangement of long extracellular loops that blocks the extracellular entrance and a helical bundle that plugs the periplasmic end (Bushell et al. 2013). Mutagenesis experiments showed that specific extracellular loops are required for in vivo capsule assembly. Wzi is a lectin that binds the K30 carbohydrate polymer. Mutants functionally deficient in vivo show no binding to K30 polymer in vitro.Apparently, Wzi is a novel outer-membrane lectin that assists in the formation of the bacterial capsule via direct interaction with capsular polysaccharides.
The outer membrane group 1 antigen capsule biogenesis/assembly protein, Wzi of 477 aas. It forms an 18 stranded beta barrel, is a lectin, and plays a role in generating the end product of capsule assembly (Rahn et al. 2003). The 2.6 Å structure reveals long extracellular loops that block the barrel entrance while a helical bundle blocks the other end of the pore (Bushell et al. 2013). Also functions as a passive bidirectional water specific porin (Sachdeva et al. 2016).
Wzi of E. coli
Uncharacterized protein of 472 aas and 22 putative β-strands and one α-TMS.
UP of Thermodesulfobacterium geofontis
Uncharacterized protein of 592 aas
UP of Syntrophobacter fumaroxidans
Uncharacterized protein of 512 aas and 16 putative β-strains and one α-TMS.
UP of Saccharophagus degradans
Uncharacterized protein of 575 aas with 13 putative β-strains and one N-terminal α-TMS.
UP of Echinicola vietnamensis
Uncharacterized protein of 498 aas with 20 putative β-strands and one N-terminal α-TMS.
UP of Dyadobacter fermentans
Uncharacterized protein of 470 aas
UP of Paludibacter propionicigenes