Research Scientist
Moraxella catarrhalis
Moraxella catarrhalis is a human pathogen that causes serious diseases such as otitis media in children and lower respiratory ailments such as chronic obstructive pulmonary disease (COPD) in the elderly. M. catarrhalis produces a surface-embedded lipooligosaccharide (LOS) that is composed of lipid A and oligosaccharide.
There are three major serotypes of M. catarrhalis, A, B and C, which have differing oligosaccharide profiles in their LOS, along with varying antigenic responses. The oligosaccharide components of these serotypes have been structurally characterised previously. Several studies, including our own have generated and used truncated forms of the oligosaccharide, to understand how the glycosyltransferases responsible for the biosynthesis of the oligosaccharide function in this biosynthetic process.
As part of our ongoing interest in understanding the assembly of both the oligosaccharide and lipid A portions of the LOS for the development of potential therapeutic agents, we have investigated the lipid A structure of a serotype B glycosyltransferase mutant LOS. Of note, the lipid A or endotoxin of serotype A wild type M. catarrhalis has previously been characterised. The resulting oligosaccharide was highly truncated as expected, however, the lipid A phosphorylation and fatty acyl chain substitution pattern of this mutant differs from that previously reported for serotype A wild type M. catarrhalis.
Heparanase
Heparanase degrades heparan sulfate (HS) chains on proteoglycans; elevated levels of heparanase expression correlate with tumour cell metastatic potential and vascularity, and reduced post-operative survival of cancer patients. Consequently, heparanase expression is considered a biomarker for cancer detection. Although several heparanase assays have been developed, most require the preparation of heterogeneous, (radio)labelled HS substrates and rely on the separation of enzymatically-degraded products on the basis of molecular size. In studies directed towards the development of a more direct heparanase assay, a series of glucuronides and glycosyl glucuronides were synthesised as putative heparanase substrates. These compounds were designed with various aryl aglycones that could be measured spectrophotometrically upon hydrolysis of the glycosidic linkage by heparanase. It was found that an N-sulfated 4-nitrophenyl glycosyl glucuronide and an N-sulfated methylumbelliferyl glycosyl glucuronide were hydrolysed by recombinant human heparanase. These compounds represent the simplest substrates of heparanase reported to date.