Post-assembly Modification of Bordetella bronchiseptica O Polysaccharide by a Novel Periplasmic Enzyme Encoded by wbmE

Jerry D King,Evgeny Vinogradov,Andrew Preston,Jianjun Li,Duncan J Maskell

doi:10.1074/jbc.m807729200

Abstract

Bordetella bronchiseptica is a pathogen of humans and animals that colonizes the respiratory tract. It produces a lipopolysaccharide O antigen that contains a homopolymer of 2,3-dideoxy-2,3-diacetamido-l-galacturonic acid (l-GalNAc3NAcA). Some of these sugars are found in the uronamide form (l-GalNAc3NAcAN), and there is no discernible pattern in the distribution of amides along the chain. A B. bronchiseptica wbmE mutant expresses an O polysaccharide unusually rich in uronamides. The WbmE protein localizes to the periplasm and catalyzes the deamidation of uronamide-rich O chains in lipopolysaccharide purified from the mutant, to attain a wild-type uronamide/uronic acid ratio. WbmE is a member of the papain-like transglutaminase superfamily, and this categorization is consistent with a deamidase role. The periplasmic location of WbmE and its acceptance of complete lipopolysaccharide as substrate indicate that it operates at a late stage in lipopolysaccharide biosynthesis, after polymerization and export of the O chain from the cytoplasm. This is the first report of such a modification of O antigen after assembly. The expression of wbmE is controlled by the Bordetella virulence gene two-component regulatory system, BvgAS, suggesting that this deamidation is a novel mechanism by which these bacteria modify their cell surface charge in response to environmental stimuli.

Highlights

Bordetella bronchiseptica is a Gram-negative coccobacillus, which colonizes the mammalian respiratory tract
LPS has three domains: first, Lipid A is the lipophilic domain that anchors LPS into the outer membrane; second, a complex, branched-chain oligosaccharide known as core is attached to lipid A and in Bordetella the lipid A-core structure is known as B-band LPS; third, a domain distal to the membrane consisting of saccharide repeats may be present, which is commonly called O antigen
The O polysaccharide consists of a homopolymer of 2,3-dideoxy-2,3-diacetamido-L-galacturonic acid (L-GalNAc3NAcA) [7] capped at the nonreducing terminus with a complex 2,3,4-trideoxy-2,3,4-triamino galacturonamide (GalN3N4NAN) derivative [8], and in B. bronchiseptica is attached to the A-band trisaccharide via a pentasaccharide linker (Fig. 1) [9]

Summary

Introduction

Bordetella bronchiseptica is a Gram-negative coccobacillus, which colonizes the mammalian respiratory tract It has a broad host range and is commonly associated with atrophic rhinitis in pigs [1] and infectious tracheobronchitis (kennel cough) in dogs [2]. Most of the genes implicated in host colonization and virulence are under the transcriptional control of the two-component regulatory system BvgAS (reviewed in Ref. 3), being expressed maximally in the Bvgϩ phase. LPS has three domains: first, Lipid A is the lipophilic domain that anchors LPS into the outer membrane; second, a complex, branched-chain oligosaccharide known as core is attached to lipid A and in Bordetella the lipid A-core structure is known as B-band LPS; third, a domain distal to the membrane consisting of saccharide repeats may be present, which is commonly called O antigen. Suicide terminated on the cytoplasmic face of the inner membrane, plasmids were based on the host-restricted pEX100T backthen exported across this membrane to the periplasmic face where the O chain is transferred to lipid A core

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Conclusion