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.

This family belongs to the Outer Membrane Pore-forming Protein I (OMPP-I) Superfamily .



Bushell, S.R., I.L. Mainprize, M.A. Wear, H. Lou, C. Whitfield, and J.H. Naismith. (2013). Wzi is an outer membrane lectin that underpins group 1 capsule assembly in Escherichia coli. Structure 21: 844-853.

Gudeman, H. and T. Dameron. (1989). Role of Hawaii State Hospital in the care of the seriously disabled mentally ill. Hawaii Med J 48: 67-69.

Rahn, A., K. Beis, J.H. Naismith, and C. Whitfield. (2003). A novel outer membrane protein, Wzi, is involved in surface assembly of the Escherichia coli K30 group 1 capsule. J. Bacteriol. 185: 5882-5890.

Sachdeva, S., N. Kolimi, S.A. Nair, and T. Rathinavelan. (2016). Key diffusion mechanisms involved in regulating bidirectional water permeation across E. coli outer membrane lectin. Sci Rep 6: 28157.


TC#NameOrganismal TypeExample

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


TC#NameOrganismal TypeExample

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