Completed Cells, Biochemistry & Physiology Genetics & Molecular Biology

Transport and polymerisation of bacterial polysaccharides: from cytoplasm to the outside world.

Funder Wellcome Charity-funded
Recipient organisation University of St Andrews
Funding £2.1M
Period Jul 2013 — Apr 2021

In plain English

AI plain-English summary

Bacteria build sugar chains on the inside of their cell membrane, then flip them to the outside to assemble protective coats that help them evade the human immune system. This project aims to understand the molecular machinery behind that process—specifically, how bacteria couple sugars to a lipid carrier, flip the units across the membrane, polymerise them into chains of precise length, and attach the finished polymer to proteins. The researchers have already expressed the key membrane proteins involved, obtained crystals of one transferase enzyme, and have preliminary data suggesting a mechanism for length control. The work fills a fundamental gap: we know these sugar coats matter for infection, but not how bacteria assemble them step by step. This is fundamental science with no immediate practical application. However, because one of the bacterial proteins resembles a human protein involved in similar sugar-handling processes, understanding the bacterial version could eventually illuminate related mechanisms in human cells. Deeper knowledge of how bacteria build their protective polysaccharide layers might also, in the longer term, suggest new targets for drugs that strip bacteria of their immune-evading shields—but that remains speculative. For now, the goal is simply to see how the molecular assembly line works.

View original technical description
Extracellular polysaccharides play a variety of roles in bacteria, most relevant to the Trust is their role in the pathogenesis of bacteria. The sugar polymers can help evade the immune system, protect against the immune response or even modulate the immune system. I wish to study the process by which sugar molecules are transported across the cytoplasmic membrane, polymerized and attached to the proteins. There are of course conceptual similarities to protein glycosylation in eukaryotes. The fi rst step of the process is coupling of sugar to a lipid carrier. There are two broad classes of integral membrane proteins that carry out this process, one of which has a similarity to human proteins. We have expressed both these integral membrane protein and propose to study both its structure and mechanism. The next step is flipping across the cytoplasm, carried out by the flippase protein. From a biochemical viewpoint this is a fascinating reaction and distinct from the ATP driven process of MsbA etc. The units are then polymerized into chain of a defined length by the polymerase, another integral membrane protein. The length of the polymer is tightly regulated and we have data to suggest a possible molecular mechanism for this. The polymer can be attached to a protein or exported or transferred to another receptor. Our focus will be on the attachment of the polymer to protein substrates. We have cloned and expressed two such transferases and have crystals of one which diffract to a round 5A.

View the original record at the funder ↗

Researchers

James Naismith (EPMC Awardee)

Related Research

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A biochemical and biophysical analysis of a ubiquitous protein translocation apparatus
Characterisation of the function and mechanism of a binding-protein dependent secondary transporter
Lipopolysaccharide translocation across the Gram-negative inner membrane; development and exploitation of reagents and knowledge to guide early stage
Barrier functions of the sugary cell coat: Understanding how extracellular signalling proteins and bacterial toxins navigate the cell surface

Original classification

Investigator Award in Science

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