Abstract
The surface O-antigen polymers of gram-negative bacteria exhibit a modal length distribution that depends on dedicated chain length regulator periplasmic proteins (polysaccharide co-polymerases, PCPs) anchored in the inner membrane by two transmembrane helices. In an attempt to determine whether structural changes underlie the O-antigen modal length specification, we have determined the crystal structures of several closely related PCPs, namely two chimeric PCP-1 family members solved at 1.6 and 2.8 Å and a wild-type PCP-1 from Shigella flexneri solved at 2.8 Å. The chimeric proteins form circular octamers, whereas the wild-type WzzB from S. flexneri was found to be an open trimer. We also present the structure of a Wzz(FepE) mutant, which exhibits severe attenuation in its ability to produce very long O-antigen polymers. Our findings suggest that the differences in the modal length distribution depend primarily on the surface-exposed amino acids in specific regions rather than on the differences in the oligomeric state of the PCP protomers.
Highlights
The length of the O-antigen polysaccharide is determined by polysaccharide co-polymerases(PCPs)
Our findings suggest that the differences in the modal length distribution depend primarily on the surface-exposed amino acids in specific regions rather than on the differences in the oligomeric state of the PCP protomers
We reported construction of several chimeric chain length regulators based on two parental WzzBs, WzzBSF and WzzBST, which share 70% amino acid identity and yet lead to distinctly different O-antigen modal length distributions [22]
Summary
The length of the O-antigen polysaccharide is determined by polysaccharide co-polymerases(PCPs). Results: We have determined structures of several chimeric PCPs that lead to different polysaccharide lengths and determined their oligomerization state. Significance: Our data provide support for the octameric assembly of WzzB PCPs. The surface O-antigen polymers of Gram-negative bacteria exhibit a modal length distribution that depends on dedicated chain length regulator periplasmic proteins (polysaccharide copolymerases, PCPs) anchored in the inner membrane by two transmembrane helices. In an attempt to determine whether structural changes underlie the O-antigen modal length specification, we have determined the crystal structures of several closely related PCPs, namely two chimeric PCP-1 family members solved at 1.6 and 2.8 Å and a wild-type PCP-1 from Shigella flexneri solved at 2.8 Å. Our findings suggest that the differences in the modal length distribution depend primarily on the surface-exposed amino acids in specific regions rather than on the differences in the oligomeric state of the PCP protomers
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