Genetics and evolution of Yersinia pseudotuberculosis O-specific polysaccharides: a novel pattern of O-antigen diversity

Abstract

O-antigen polysaccharide is a major immunogenic feature of the lipopolysaccharide of Gram-negative bacteria, and most species produce a large variety of forms that differ substantially from one another. There are 18 known O-antigen forms in the Yersinia pseudotuberculosis complex, which are typical in being composed of multiple copies of a short oligosaccharide called an O unit. The O-antigen gene clusters are located between the hemH and gsk genes, and are atypical as 15 of them are closely related, each having one of five downstream gene modules for alternative main-chain synthesis, and one of seven upstream modules for alternative side-branch sugar synthesis. As a result, many of the genes are in more than one gene cluster. The gene order in each module is such that, in general, the earlier a gene product functions in O-unit synthesis, the closer the gene is to the 5΄ end for side-branch modules or the 3΄ end for main-chain modules. We propose a model whereby natural selection could generate the observed pattern in gene order, a pattern that has also been observed in other species.

Wzx flippases exhibiting complex O‐unit preferences require a new model for Wzx–substrate interactions

“…S2). The wzx 3 and wzx 8 genes represent the other two wzx types found within the 14‐related Y. pseudotuberculosis O‐antigen gene clusters, whereas wzx 4 and wzx 5 are from unrelated gene clusters (Kenyon et al., ).…”

“…A group of 14 closely‐related Yersinia pseudotuberculosis O‐antigen gene clusters with four unique wzx sequence types, which produce O units with one of six alternative main‐chains and one of seven alternative side‐branch residues (Kenyon, Cunneen, & Reeves, ), represent a rare opportunity to expand our understanding of Wzx substrate preference. Within this set, the O:1a, O:2a, and O:4b O units (Figure a) consist of three shared residues (GlcNAc, galactose (Gal) and 6‐deoxymannoheptose (6dManHep)) with identical linkages, and one of three different terminal dideoxyhexose (DDH) residues (paratofuranose (Par f ), O:1a; abequose (Abe p ), O:2a; tyvelose (Tyv p ), O:4b) attached via an α(1,3) (O:2a, O:4b) or β(1,3) (O:1a) linkage by different GTs (WbyA, O:2a/O:4b; WbyM, O:1a).…”

“…The corresponding O‐antigen gene clusters (Figure a) differ only in the genes responsible for DDH synthesis and attachment, and interestingly, contain one of two unrelated wzx genes ( wzx 1 , O:1a; wzx 2 , O:2a/O:4b). These wzx are notably found in 12 of the 14 related gene clusters, and are exclusively associated with specific terminal DDH or DDH‐like residues (altrofuranose (Alt f ), Par f or ascarylose (Asc p ) with wzx 1 ; Abe p or Tyv p with wzx 2 ) on different O‐unit main‐chains (two main‐chains associated with both wzx , three main‐chains associated with only one wzx ) (Kenyon et al., ) (Figure b). In this study we describe the cloning and manipulation of the Y. pseudotuberculosis O:1a, O:2a and O:4b O‐antigen gene clusters for expression in E. coli , and the use of these clones to conclusively demonstrate that both Wzx 1 and Wzx 2 show a strong preference for specific terminal DDH residues.…”

“…This figure is adapted from Kenyon et al. (). (b) Full range of Y. pseudotuberculosis O units translocated by the Wzx 1 and Wzx 2 flippases.…”

“…A group of 14 closely-related Yersinia pseudotuberculosis Oantigen gene clusters with four unique wzx sequence types, which produce O units with one of six alternative main-chains and one of seven alternative side-branch residues (Kenyon, Cunneen, & Reeves, 2017), represent a rare opportunity to expand our un-…”