title: The Arabidopsis COBRA protein facilitates cellulose crystallization at the plasma membrane.
abstract: Mutations in the Arabidopsis COBRA gene lead to defects in cellulose synthesis but the function of COBRA is unknown. Here we present evidence that COBRA localizes to discrete particles in the plasma membrane and is sensitive to inhibitors of cellulose synthesis, suggesting that COBRA and the cellulose synthase complex reside in close proximity on the plasma membrane. Live-cell imaging of cellulose synthesis indicated that, once initiated, cellulose synthesis appeared to proceed normally in the cobra mutant. Using isothermal calorimetry, COBRA was found to bind individual β1-4-linked glucan chains with a KD of 3.2 μm. Competition assays suggests that COBRA binds individual β1-4-linked glucan chains with higher affinity than crystalline cellulose. Solid-state nuclear magnetic resonance studies of the cell wall of the cobra mutant also indicated that, in addition to decreases in cellulose amount, the properties of the cellulose fibrils and other cell wall polymers differed from wild type by being less crystalline and having an increased number of reducing ends. We interpret the available evidence as suggesting that COBRA facilitates cellulose crystallization from the emerging β1-4-glucan chains by acting as a "polysaccharide chaperone."
authors.affiliation: From the Energy Biosciences Institute, the Plant and Microbial Biology Department, and nadavsorek@berkeley.edu.
authors.forename: Nadav
authors.initials: N
authors.lastname: Sorek
authors.affiliation: From the Energy Biosciences Institute.
authors.forename: Hagit
authors.initials: H
authors.lastname: Sorek
authors.affiliation: the Department of Chemistry, University of California, Berkeley, California 94720.
authors.forename: Aleksandra
authors.initials: A
authors.lastname: Kijac
authors.affiliation: From the Energy Biosciences Institute, the Plant and Microbial Biology Department, and.
authors.forename: Heidi J
authors.initials: HJ
authors.lastname: Szemenyei
authors.affiliation: From the Energy Biosciences Institute.
authors.forename: Stefan
authors.initials: S
authors.lastname: Bauer
authors.affiliation: the INRA, Institut Jean-Pierre Bourgin, UMR 1318, ERL CNRS3559, Saclay Plant Sciences, RD10, F-78026 Versailles, France, AgroParisTech, Institut Jean-Pierre Bourgin, UMR 1318, ERL CNRS3559, Saclay Plant Sciences, RD10, F-78026 Versailles, France, and.
authors.forename: Kian
authors.initials: K
authors.lastname: Hématy
authors.affiliation: From the Energy Biosciences Institute, the Department of Chemistry, University of California, Berkeley, California 94720.
authors.forename: David E
authors.initials: DE
authors.lastname: Wemmer
authors.affiliation: From the Energy Biosciences Institute, the Plant and Microbial Biology Department, and Department of Arid Land Agriculture, Faculty of Meteorology, Environment and Arid Land Agriculture, King Abdulaziz University, 21589 Jeddah, Saudi Arabia.
authors.forename: Chris R
authors.initials: CR
authors.lastname: Somerville
mesh_terms: D017360:Arabidopsis / Q000166:cytology* / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism*; D002473:Cell Wall / Q000378:metabolism; D002482:Cellulose / Q000737:chemistry*; D003460:Crystallization; D005936:Glucans / Q000737:chemistry / Q000378:metabolism; D008562:Membrane Glycoproteins / Q000378:metabolism*; D057054:Molecular Imaging; D021381:Protein Transport
chemical_list: D029681:Arabidopsis Proteins; C427475:COB protein, Arabidopsis; D005936:Glucans; D008562:Membrane Glycoproteins; D002482:Cellulose; C040088:1,4-glucan
keywords: Arabidopsis COBRA; Cellulose; Cellulose Biosynthesis; Isothermal Titration Calorimetry (ITC); Plant Biochemistry; Plant Cell Wall; Solid State NMR