Structure and function of invertebrate Golgi hexosaminidases

Hexosaminidases are ubiquituous enzymes with multiple roles in glycoconjugate metabolism as they remove terminal N-acetylhexosamine residues from glycans, glycolipids, glycoproteins and glycosaminoglycans; whereas these enzymes are catabolic in mammals, in non-vertebrate species they are often mediating purposeful processing steps during the maturation of N-linked oligosaccharides on proteins (analogous to mannosidases in the endoplasmic reticulum and Golgi apparatus). However, the biological significance of, and the structural basis for, hexosaminidase-mediated glycan-processing in non-vertebrates are poorly understood. In this proposal project, the aim is to understand the substrate specificity of nematode and insect hexosaminidases in terms of the amino acid residues involved in recognition/catalysis and explore whether deletion of nematode hexosaminidase genes has an effect on responses to stress and infection. Convergent evolution may explain that phylogentically-diverse insect and nematode hexosaminidases have the same glycan processing function.

Hexosaminidases are ubiquituous enzymes with multiple roles in glycoconjugate metabolism as they remove terminal N-acetylhexosamine residues from glycans, glycolipids, glycoproteins and glycosaminoglycans; whereas these enzymes are catabolic in mammals, in non-vertebrate species they are often mediating purposeful processing steps during the maturation of N-linked oligosaccharides on proteins (analogous to mannosidases in the endoplasmic reticulum and Golgi apparatus). However, the biological significance of, and the structural basis for, hexosaminidase-mediated glycan-processing in non-vertebrates are poorly understood. In this project, we have identified hexosaminidase genes from parasitic nematodes and characterised one such hexosaminidase in recombinant form, comparing its properties to those from other species. Furthermore, the impact of knocking-out hexosaminidase genes in the model organism, Caenorhabditis elegans, was assessed. An obvious molecular change in terms of the N-linked oligosaccharides was observed showing that multiple hexosaminidases alter these structures and so determine the final form of post-translational modifications of proteins.