Biosynthesis and Assembly of Capsular Polysaccharides in Escherichia coli

Abstract

Capsules are protective structures on the surfaces of many bacteria. The remarkable structural diversity in capsular polysaccharides is illustrated by almost 80 capsular serotypes in Escherichia coli. Despite this variation, the range of strategies used for capsule biosynthesis and assembly is limited, and E. coli isolates provide critical prototypes for other bacterial species. Related pathways are also used for synthesis and export of other bacterial glycoconjugates and some enzymes/processes have counterparts in eukaryotes. In gram-negative bacteria, it is proposed that biosynthesis and translocation of capsular polysaccharides to the cell surface are temporally and spatially coupled by multiprotein complexes that span the cell envelope. These systems have an impact on both a general understanding of membrane trafficking in bacteria and on bacterial pathogenesis.

Comparative genomics analyses on EPS biosynthesis genes required for floc formation of Zoogloea resiniphila and other activated sludge bacteria

“…The activated sludge EPS might be a mixture of polysaccharides of multiple bacteria. Despite the diversity in bacterial glycoconjugates, bacteria may use a limited repertoire of biosynthesis and assembly strategies (Whitefield, 2006). Based on the organization of the identified EPS gene cluster, it is predicted that the biosynthesis and assembly of EPS in Zoogloea occur in a similar manner to the Wzy-dependent synthesis of capsular polysaccharide in Escherichia coli.…”

Sequence-structure relationships in polysaccharide co-polymerase (PCP) proteins

“…The biosynthesis of many lipopolysaccharide (LPS) O-antigens (Oags), enterobacterial common antigen (ECA) and some capsule polysaccharides (CPSs) in Gram-negative and Gram-positive bacteria occurs by a mechanism known as the Wzy polymerasedependent pathway [1][2][3][4]. The process relies on a putative, multifunctional protein complex involving homologues of the inner membrane proteins Wzx, Wzy and Wzz [5].…”

“…The PCP1 and PCP2 proteins participate in the Wzy-dependent pathway of polysaccharide biosynthesis, whereas the PCP3 proteins are involved in CPS biosynthesis via an ABC-2 type transporter pathway (for a review, see Ref. [4]). Additionally, the PCP1 group is divided into PCP1a and PCP1b, distinguishing the WzzB proteins (PCP1a) that operate on Oag from the WzzE proteins (PCP1b) that regulate the length of ECA [1].…”

“…Wzc is an inner membrane protein that is required in E. coli for the biosynthesis of high molecular weight group 1 polysaccharides in a process coupled to export via contacts with the OMP Wza [4]. Single particle averaging of Wzc, phosphorylated on the cytoplasmic domain, from CEM images indicate that it forms a tetramer, with contacts between the periplasmic domains forming a nearly sealed chamber above the inner membrane [4]. Unlike Wzz proteins, Wzc has a cytoplasmic C-terminal domain with tyrosine kinase activity and an ATP-binding motif [26,27].…”

“…The PCP3 family is associated with capsule biosynthesis using the ABC-2 type transporter biosynthesis pathway. KpsE is part of a protein complex responsible for group 2 capsule biosynthesis in E. coli [4,38]. Two TM helices are predicted within this 382 residue-long protein that contains a 310 residuelong periplasmic region.…”