Polysaccharide

Event Date: 
Wednesday, March 27, 2013 - 18:00 - 18:15
Institution: 
University of Sydney
Title: 

Insight into the specificity of Wzx for O-antigen processing

Abstract: 

Most Gram-negative bacteria have an O antigen that consists of repeats of 3-6 sugars, and serve as an essential factor for host colonization in many disease-causing bacteria. Until now, most known O antigens are assembled by the Wzx/Wzy pathway. This involves the assembly of repeat units within the cytoplasmic face of inner membrane on a lipid carrier, undecaprenol-phosphate, which are translocated across membrane by the Wzx translocases. In the periplasmic face, the repeat units are polymerized by the Wzy polymerase, and then subsequently ligated to preformed lipid A-core in the periplasm. Earlier works have shown Wzx translocases have a relax specificity requirement over the repeat-unit structures. However, this could neither correlate to the presence of O antigen with defined structures in each respective bacteria, nor could it explain the biological diversity of Wzx translocases. Our data show that Wzx translocases have a serotype specificity over their native repeat-unit structures, and provides evidence that the earlier conclusion were obscured by protein overexpression. This provides relevant explanation to the presence of highly diverse, yet structurally defined bacterial surface polysaccharides in nature.

JAMS REPORT
Ani Penesyan
 
On the last Wednesday of spring we were spoiled with the room on the top floor of the Australian Museum and magnificent views of Sydney, yes, once again! Joining us were not only our regular JAMS crowd, but also visitors from Europe (yes, that is really cold in Europe during this time of the year!)
 

Event Date: 
Wednesday, November 28, 2012 - 06:15 - 06:30
Institution: 
University of Sydney
Title: 

Does Acinetobacter baumannii have an O antigen?

Abstract: 

 
Acinetobacter baumannii is amongst the most troublesome Gram-negative pathogens worldwide, due to strains that are resistant to multiple antibiotics, disinfection and periods of desiccation. Little is known about the virulence mechanisms, though a role for capsule has been demonstrated. Previous analysis of A. baumannii genome sequences identified a region of extensive diversity presumed to be involved in the synthesis of a surface polysaccharide, variously identified as O-antigen or capsule. We used bioinformatic tools to assess whether this polysaccharide is exported as capsule, or ligated to a lipid A-core oligosaccharide moiety to become the O antigen moiety of lipopolysaccharide. A gene for O-antigen ligase was not found, and we propose that A. baumannii strains produce a capsule (and lipid A-core oligosaccharide), but no lipopolysaccharide.  9 capsule types and 3 core types were found in the 10 completed genomes and more in draft genomes. Multiple capsule types were found in members of the 2 major clonal complexes, and this variation may contribute to the success of the A. baumannii clones by factoring in the evasion of the host immune response.

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