Identification and characterisation of chitin and cellulose synthases in oomycetes
New tools for biochemical studies and structure determination
Time: Fri 2021-11-26 10.00
Subject area: Biotechnology
Doctoral student: Stefan Klinter , Glykovetenskap
Opponent: Dr. Mirjam Czjzek, SNRS/ Sorbonne University
Supervisor: Professor Vincent Bulone, Glykovetenskap; Docent Lauren S. McKee, Glykovetenskap, Wallenberg Wood Science Center
Despite resembling ‘true’ fungi in terms of morphological features, oomycetes form a distinct eukaryotic lineage of filamentous microorganisms that belongs to the stramenopiles, a group of protists also comprising the closely-related brown algae and diatoms. Many oomycetes are devastating pathogens of plants and animals, globally causing significant economic losses in the agriculture and aquaculture industries, and posing considerable environmental damage to natural ecosystems. Although the cell wall (CW) is critical for the viability and morphogenesis of the organism it surrounds, our knowledge of oomycete CW architecture and biosynthetic enzymes is limited. Given the vast threat that pathogenic oomycetes pose, uncovering the details of CW biosynthesis and regulation in these pathogens may reveal new opportunities for disease control.
To this end, we aimed to elucidate the role of putative membrane-bound glycosyltransferase family 2 enzymes implicated in the biosynthesis of oomycete CW polysaccharides. Suitable gene candidates were identified, and their products analysed, as illustrated by the oomycete-wide discovery and phylogenetic analysis of the chitin synthase gene family (paper I), and the identification of the cellulose synthase genes in Saprolegnia parasitica (paper II) and Phytophthora capsici (paper III). Expression of promising candidate genes was verified using different techniques, including gene expression analysis (papers II and III), and the effect of inhibitors on hyphal growth (papers I and II) and enzymatic activity in in vitro assays (paper II). Single enzymes representing putative chitin synthases from various organisms (unpublished data) and cellulose synthases from S. parasitica (extended data for paper II), and P. capsici cellulose synthase 1 (paper III) were produced, and partly enriched or even purified, in yeast strains specifically engineered to facilitate the biochemical characterisation of the recombinant proteins in in vitro enzyme assays. To advance functional investigations and structure determination of integral membrane proteins, we developed DirectMX, a method that allows the reconstitution of target proteins with their surrounding lipids directly from crude cell membranes into Salipro nanoparticles (paper IV).