A Bipartite Glucan Synthase-Remodeler Module Organizes Branched Glucan Assembly in the Fungal Cell Wall

Abstract The fungal cell wall is an essential extracellular matrix that underpins growth, morphogenesis, and pathogenesis. Cell wall construction requires numerous enzymes that synthesize and remodel extracellular polymers, yet the principles governing their spatial and functional organization remain unclear. In the fission yeast Schizosaccharomyces pombe , we identify Ghs2, a predicted glycoside hydrolase 16 (GH16) domain-containing transmembrane protein, as an obligate binding partner of the β-1,3-glucan synthase Bgs3. Ghs2 and Bgs3 co-localize at sites of polarized growth and physically associate in vivo . Structure-guided modeling positions the Ghs2 GH16 domain proximal to the predicted Bgs3 glucan extrusion pore, suggesting coordinated polymer synthesis and remodeling. Solid-state NMR analyses demonstrate that both Ghs2 and Bgs3 are required for the proper accumulation of branched β-1,3-glucan. Together with genetic and cell biological evidence, these findings support a model in which Bgs3 synthesizes linear β-1,3-glucan and Ghs2 subsequently introduces β-1,6-linked branch points onto the nascent polymer. More broadly, we propose that synthase-modifier pairs may act together to shape polymer architecture during cell wall assembly.