Structures of Lipopolysaccharides from Klebsiella pneumoniae

Abstract

Deamination of LPSs from Klebsiella pneumoniae released O-chain polysaccharides together with a fragment of the core oligosaccharide. The structures of the products from serotypes O1, O2a, O2a,c, O3, O4, O5, and O12 were determined by NMR spectroscopy and chemical methods, identifying the linkage region between the O antigens and the core as well as novel residues at the non-reducing ends of the polysaccharides. All serotypes had an identical linkage between the O chain and core.Like other members of the family Enterobacteriaceae, the lipopolysaccharides (LPSs) 1 of Klebsiella pneumoniae consist of three structural domains, (i) the hydrophobic lipid A, which is a major component of the outer leaflet of the Gram-negative outer membrane, and (ii) the core oligosaccharide, which is linked to lipid A and provides the attachment site for (iii) the long chain polysaccharide (O antigen; O chain). Typically, structural diversity is greater in the regions of LPS extending from the cell surface (i.e. the O chains). Varying chemical structures in the O chains gives rise to a number of serologically distinct O antigens. In the Klebsiellae there are 11 known O-chain structures, but structural similarities lead to some serological cross-reactivities, so the actual number of unique O serotypes is less (1, 2). Several of the O-antigens are based on a structure designated D-galactan I with a repeat unit compris-2 When present alone, this structure provides the 2a antigen (3), but it can be capped by additional structural domains or modified by side chain acetyl or galactosyl residues to generate additional unique antigens (3-6). For example, in the most clinically prevalent serotype, the O1 antigen, D-galactan I chains are capped by a domain with a different repeat unit structure, [-. Genetic (7) and chemical (8, 9) analyses indicate that D-galactan I chains are linked directly to the lipid A core structure, whereas D-galactan II is confined to the distal end of some of the available D-galactan I chains (10). D-Galactan II provides the epitope(s) that defines the O1 antigen (9), and its presence is required for the resistance of the bacteria to complement-mediated killing in the host; K. pneumoniae mutants that only produce D-galactan I are therefore serum-sensitive (11, 12). However, not all Klebsiella O serotypes are based on D-galactan I. The prevalent O3 and O5 serotypes comprise mannan O chains with structures identical to the Escherichia coli O9 and O8 antigens, respectively (13,14). The remaining Klebsiella O-chain structures are heteropolymers.The biosynthesis of the polysaccharide O chain has been investigated in some serotypes of K. pneumoniae by biochemical and genetic experimental approaches. Much of the data for the O3 and O5 serotypes is derived from the related equivalent systems in E. coli. However, the genetic loci required for synthesis of the corresponding O chain structures in E. coli (O8 ec and O9 ec ) and K. pneumoniae (O5 kp and O3 kp , respectively) are essentially identical and reflect lateral gene trans...

Nonreducing Terminal Modifications Determine the Chain Length of Polymannose O Antigens of Escherichia coli and Couple Chain Termination to Polymer Export via an ATP-binding Cassette Transporter

“…1) and convert serotype O9 to O9a (19). The primer, adaptor, and repeat-unit domains are clearly identified in structural studies of the LPSs (13). In this report we demonstrate that the WbdD proteins control the chain length of the E. coli O8 and O9a polymannans by modifying the nonreducing end of nascent und-PP-linked polymer.…”

“…Structure and biosynthesis of the polymannan O-PSs. A, the structure and organization of the polymers was established by analysis of the K. pneumoniae LPSs, where both the reducing terminal GlcNAc residue and the adapter dimannose structure were identified (13). The repeating unit is enclosed by square brackets.…”

“…1). The polymannans have nonreducing terminal O-methyl groups (13,14). Identical O-PS structures and gene clusters are found in Klebsiella pneumoniae O3 (E. coli O9) and K. pneumoniae O5 (E. coli O8) as a result of lateral gene transfer (15).…”

“…Structural and biosynthetic data for the E. coli and K. pneumoniae analogs are interchangeable. The mechanistic details of assembling the E. coli O8 and O9a O-PSs on the lipid carrier have not been fully elucidated, but a working biosynthetic model has been proposed based on the available structural and genetic evidence (13,16). O-PS synthesis begins with the conserved formation of a "primer" by transfer of a GlcNAc-1-phosphate residue to und-P.…”

“…Recent structural analysis has identified novel residues at the nonreducing end of some O-PSs synthesized by the ABC transporter-dependent pathway (Ref. 13 and the references therein). Here we describe for the first time the role played by these nonreducing terminal modifications in O-PS chain termination.…”