Wide-Angle X-Ray Scattering and Solid-State Nuclear Magnetic Resonance Data Combined to Test Models for Cellulose Microfibrils in Mung Bean Cell Walls

Abstract

A synchrotron wide-angle x-ray scattering study of mung bean (Vigna radiata) primary cell walls was combined with published solid-state nuclear magnetic resonance data to test models for packing of (1→4)-b-glucan chains in cellulose microfibrils. Computersimulated peak shapes, calculated for 36-chain microfibrils with perfect order or uncorrelated disorder, were sharper than those in the experimental diffractogram. Introducing correlated disorder into the models broaden the simulated peaks but only when the disorder was increased to unrealistic magnitudes. Computer-simulated diffractograms, calculated for 24-and 18-chain models, showed good fits to experimental data. Particularly good fits to both x-ray and nuclear magnetic resonance data were obtained for collections of 18-chain models with mixed cross-sectional shapes and occasional twinning. Synthesis of 18-chain microfibrils is consistent with a model for cellulose-synthesizing complexes in which three cellulose synthase polypeptides form a particle and six particles form a rosette.

A Structural Study of CESA1 Catalytic Domain of Arabidopsis Cellulose Synthesis Complex: Evidence for CESA Trimers

“…Recent studies of cellulose structure have estimated 18 to 24 glucan chains per microfibril (Fernandes et al, 2011;Newman et al, 2013), contrary to the more widely accepted value of a 36 mer of glucan chains comprising a microfibril (Herth, 1983;Delmer, 1999;Doblin et al, 2002). As a consequence, the stoichiometry of the cellulose synthase complex has been revisited, and there is speculation that the individual particles of the hexameric rosette, identified in TEM studies, could contain as few as three CESA proteins (Newman et al, 2013;Hill et al, 2014).…”

“…Further, it has been recently reported that the stoichiometry of CESAs 1, 3, and 6 and CESAs 4, 7, and 8 in the primary and secondary cell walls, respectively, is 1:1:1 (Gonneau et al, 2014;Hill et al, 2014). Together, these reports suggest a rosette CSC composed of 18 CESA proteins with three CESAs per lobe as the most likely composition of a rosette CSC to account for an 18-chain cellulose microfibril (Newman et al, 2013;Gonneau et al, 2014;Hill et al, 2014). In addition, it should also be noted that 24 CESA proteins in a rosette CSC with four proteins per lobe is incompatible with a 1:1:1 CESA stoichiometry.…”

“…However, recent studies using different analytical techniques combined with computation report 18 to 24 cellulose chains per microfibril (Fernandes et al, 2011;Thomas et al, 2013;Oehme et al, 2015). A study of cellulose from mung bean (Vigna radiata) primary cell walls, using x-ray diffraction, solid-state NMR, and computational analysis, supports an 18-chain model for a cellulose microfibril (Newman et al, 2013). This implies that the CSC is composed of fewer than 36 CESA proteins or that not all of the proteins in a CSC are simultaneously active.…”

“…This model structure aligns well with the crystal structure of the bacterial cellulose synthase, indicating that a common mechanism exists for cellulose synthesis in bacteria and plants and that CESAs within rosette CSCs contain a single active synthetic site. In addition, this model made it possible to test possible configurations for the assembly of CESA monomers into a functional rosette CSC (Newman et al, 2013;Sethaphong et al, 2013).…”

Relationships between Biomass Composition and Liquid Products Formed via Pyrolysis

“…Cellulose is an unbranched homopolymer of >500 β-(1,4)-linked glucose units. In plant cell walls, cellulose is primarily in the form of crystalline microfibrils consisting of approximately 36 hydrogen-bonded cellulose chains, but also has amorphous regions (Somerville, 2006;Newman et al, 2013).…”