Protein glycosylation in the gram-negative gamma proteobacterium photorhabdus luminescens
Fox, Mary Elizabeth (2011) Protein glycosylation in the gram-negative gamma proteobacterium photorhabdus luminescens. PhD thesis, Dublin City University.
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The objective of this research was to investigate the possibility that Photorhabdus luminescens produces glycoproteins and thus contains a protein glycosylation system. P. luminescens is a pathogen of insects and a symbiont of soil nematodes. Adhesion and invasion are very important in the life cycle of the organism and it is speculated that the bacteria may produce glycoproteins to facilitate infection of the host.
Proteins from P. luminescens were analysed using lectins for the presence of glycoproteins. Many potential glycoproteins were isolated using lectin affinity chromatography (LAC) and one such protein was identified conclusively using mass spectrometry to be an outer membrane porin, OmpN. No glycoproteins have previously been identified in P. luminescens. The ompN gene was cloned and expressed in both Escherichia coli and P. luminescens. It was found that OmpN purified from P. luminescens was capable of binding the lectins WGA and GSL I, while OmpN purified from E. coli was not.
Campylobacter jejuni is the most extensively studied bacteria in terms of protein glycosylation. It contains a pgl locus encoding enzymes involved in the glycosylation of many of its proteins. Orthologues of some Pgl proteins were discovered in P. luminescens. The gene that encodes one of these proteins, wblK, was mutated. LAC was used to examine the effect of this mutation on the glycoproteins produced by the organism. It was found that the glycosylation of at least two proteins was affected by the wblK mutation. These proteins were isolated by LAC using WGA agarose from the wblK mutant strain but not from the wildtype strain. One of the altered proteins was identified as plu3611. It was found to exist in at least two different glycoforms. The results provided evidence that P. luminescens is capable of glycosylating OmpN and plu3611 and so contains a protein glycosylation system.
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