Multidimensional solid‐state NMR studies of the structure and dynamics of pectic polysaccharides in uniformly ¹³C‐labeled Arabidopsis primary cell walls

Abstract

Plant cell wall (CW) polysaccharides are responsible for the mechanical strength and growth of plant cells; however, the high-resolution structure and dynamics of the CW polysaccharides are still poorly understood because of the insoluble nature of these molecules. Here, we use 2D and 3D magic-angle-spinning (MAS) solid-state NMR (SSNMR) to investigate the structural role of pectins in the plant CW. Intact and partially depectinated primary CWs of Arabidopsis thaliana were uniformly labeled with (13)C and their NMR spectra were compared. Recent (13)C resonance assignment of the major polysaccharides in Arabidopsis thaliana CWs allowed us to determine the effects of depectination on the intermolecular packing and dynamics of the remaining wall polysaccharides. 2D and 3D correlation spectra show the suppression of pectin signals, confirming partial pectin removal by chelating agents and sodium carbonate. Importantly, higher cross peaks are observed in 2D and 3D (13)C spectra of the depectinated CW, suggesting higher rigidity and denser packing of the remaining wall polysaccharides compared with the intact CW. (13)C spin-lattice relaxation times and (1)H rotating-frame spin-lattice relaxation times indicate that the polysaccharides are more rigid on both the nanosecond and microsecond timescales in the depectinated CW. Taken together, these results indicate that pectic polysaccharides are highly dynamic and endow the polysaccharide network of the primary CW with mobility and flexibility, which may be important for pectin functions. This study demonstrates the capability of multidimensional SSNMR to determine the intermolecular interactions and dynamic structures of complex plant materials under near-native conditions.

Folding of xylan onto cellulose fibrils in plant cell walls revealed by solid-state NMR

“…indicating the relative rigidity of the polysaccharides and a range of different environments. As expected, the major peaks in the spectrum are from glucose in the two main cellulose environments (C 1 : often assigned to crystalline and/or internal glucan chains; and C 2 : often assigned to amorphous and/or surface glucan chains)8910111228. Surprisingly, two distinct xylan carbon 4 (Xn4) peaks are clearly visible in the spectrum (82.2 and 77.4 p.p.m.…”

“…Xyloglucan was thought to crosslink microfibrils in primary cell walls. Multidimensional MAS NMR analyses of primary cell walls, pioneered in recent years by Hong and colleagues, have shown that, in contrast, only a minor portion of xyloglucan interacts with cellulose891011121314. In secondary cell walls, xylan (Supplementary Fig.…”

Re-constructing our models of cellulose and primary cell wall assembly

“…Based on ssNMR spin diffusion, ∼50% of the cellulose surface makes contact with pectin [67]. Partial extraction of pectin from Arabidopsis cell walls rigidified the remaining matrix polysaccharides [67] and greatly slowed magnetic spin transfer from water to cellulose [68]. The latter result was attributed to water stabilization by pectins (spin transfer is reduced by rapid motions of water).…”

Multidimensional solid-state NMR spectroscopy of plant cell walls

“…In comparison, matrix polysaccharides are much more mobile. For example, while 13 C T 1 relaxation times of cellulose are 5–10 s at 14.1–18.8 Tesla, matrix polysaccharides exhibit much shorter 13 C T 1 relaxation times of ~1 s [6, 14, 15]. Interestingly, the pectin T 1 relaxation is heterogeneous with at least two components: a fast component of ~0.4 s and a slow component of ~5 s (Fig.…”