Insights into substrate coordination and glycosyl transfer of poplar cellulose synthase-8

• Published in: Structure (London) Vol. 31; no. 10; pp. 1166 - 1173.e6
• Main Authors: Verma, Preeti, Kwansa, Albert L., Ho, Ruoya, Yingling, Yaroslava G., Zimmer, Jochen
• Format: Journal Article
• Language: English
• Published: United States Elsevier Ltd 05-10-2023
• Subjects: cellulose biosynthesis; cryo-electron microscopy; glycosyltransferase; molecular dynamics simulations; mutagenesis; molecular dynamics simulations; mutagenesis; glycosyltransferase; cellulose biosynthesis; cryo-electron microscopy
• ISSN: 0969-2126; 1878-4186
• DOI: 10.1016/j.str.2023.07.010

Cellulose is an abundant cell wall component of land plants. It is synthesized from UDP-activated glucose molecules by cellulose synthase, a membrane-integrated processive glycosyltransferase. Cellulose synthase couples the elongation of the cellulose polymer with its translocation across the plasma membrane. Here, we present substrate- and product-bound cryogenic electron microscopy structures of the homotrimeric cellulose synthase isoform-8 (CesA8) from hybrid aspen (poplar). UDP-glucose binds to a conserved catalytic pocket adjacent to the entrance to a transmembrane channel. The substrate’s glucosyl unit is coordinated by conserved residues of the glycosyltransferase domain and amphipathic interface helices. Site-directed mutagenesis of a conserved gating loop capping the active site reveals its critical function for catalytic activity. Molecular dynamics simulations reveal prolonged interactions of the gating loop with the substrate molecule, particularly across its central conserved region. These transient interactions likely facilitate the proper positioning of the substrate molecule for glycosyl transfer and cellulose translocation.
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•Cryo-EM structure of UDP-glucose-bound poplar cellulose synthase-8•Site-directed mutagenesis analyzes the function of a flexible gating loop•Conserved gating loop residues are necessary for cellulose biosynthesis•Molecular dynamics simulations support persistent gating loop-substrate interactions
Verma et al. determined the cryo-electron microscopy structure of UDP-glucose-bound poplar cellulose synthase-8 that provides insights into substrate selectivity and glycosyl transfer. Site-directed mutagenesis of a conserved but structurally flexible gating loop reveals residues critical for cellulose biosynthesis. Molecular dynamics simulations of substrate-bound cellulose synthase-8 reveal direct gating loop-substrate interactions.