Cellulose Microfibril Twist, Mechanics, and Implication for Cellulose Biosynthesis

Zhao, Zhen; Shklyaev, Oleg E.; Nili, Abdolmajid; Mohamed, Mohamed Naseer Ali; Kubicki, James D.; Crespi, Vincent H.; Zhong, Linghao

doi:10.1021/jp3089929

Cited by 88 publications

(102 citation statements)

References 68 publications

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“…The slight twist of the protein surface suggests that EXLX1 may have a preference to bind to cellulose surfaces with a similar twist. Computational studies indicate that cellulose microfibrils develop a right-handed twist (Zhao et al 2013), but it is not as steep as that seen in the expansin-ligand crystals. Hence BsEXLX1 may selectively bind to a microfibril site with a more accentuated twist than is generally the case.…”

Section: Structure-function Analysis Of Bacterial Expansins and Theirmentioning

confidence: 99%

Bacterial expansins and related proteins from the world of microbes

Georgelis

Nikolaidis

Cosgrove

2015

Appl Microbiol Biotechnol

109

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The discovery of microbial expansins emerged from studies of the mechanism of plant cell growth and the molecular basis of plant cell wall extensibility. Expansins are wall-loosening proteins that are universal in the plant kingdom and are also found in a small set of phylogenetically diverse bacteria, fungi, and other organisms, most of which colonize plant surfaces. They loosen plant cell walls without detectable lytic activity. Bacterial expansins have attracted considerable attention recently for their potential use in cellulosic biomass conversion for biofuel production, as a means to disaggregate cellulosic structures by non-lytic means (‘amorphogenesis’). Evolutionary analysis indicates that microbial expansins originated by multiple horizontal gene transfers from plants. Crystallographic analysis of BsEXLX1, the expansin from Bacillus subtilis, shows that microbial expansins consist of two tightly-packed domains: the N-terminal domain D1 has a double-ψ β-barrel fold similar to glycosyl hydrolase family-45 enzymes, but lacks catalytic residues usually required for hydrolysis; the C-terminal domain D2 has a unique β-sandwich fold with three co-linear aromatic residues that bind β-1,4-glucans by hydrophobic interactions. Genetic deletion of expansin in Bacillus and Clavibacter cripples their ability to colonize plant tissues. We assess reports that expansin addition enhances cellulose breakdown by cellulase and compare expansins with distantly related proteins named swollenin, cerato-platanin and loosenin. We end in a speculative vein about the biological roles of microbial expansins and their potential applications. Advances in this field will be aided by a deeper understanding of how these proteins modify cellulosic structures.

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Section: Structure-function Analysis Of Bacterial Expansins and Theirmentioning

confidence: 99%

Bacterial expansins and related proteins from the world of microbes

Georgelis

Nikolaidis

Cosgrove

2015

Appl Microbiol Biotechnol

109

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“…The fibrils were highly disordered, probably as a result of the limited number of chains used for the simulation. Other work indicates that 6 chains may be too few to form a stable structure resembling native cellulose [46]. One novel result to emerge from the MDS was the accumulation of noncrystallized glucan chains at the outer surface of the CSC prior to formation of a protofibril.…”

Section: Cellulose Microfibril Synthesis and Guidancementioning

confidence: 99%

“…This stems in part from the thinness of the microfibril and the conformational disorder of surface chains, which are more dynamic and flexible than the more-constrained internal chains, and in part from sloppy packing of internal chains [34]. The internal disorder may arise from twisting of the microfibril and the resulting need to periodically relieve the internal stress [46]. It may also arise from entrapment of xyloglucan within the microfibril – an attractive idea that dates from the 1980's [49] but still has only circumstantial support.…”

Section: Cellulose Microfibril Synthesis and Guidancementioning

confidence: 99%

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

Cosgrove

2014

Current Opinion in Plant Biology

367

303

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The cellulose microfibril has more subtlety than is commonly recognized. Details of its structure may influence how matrix polysaccharides interact with its distinctive hydrophobic and hydrophilic surfaces to form a strong yet extensible structure. Recent advances in this field include the first structures of bacterial and plant cellulose synthases and revised estimates of microfibril structure, reduced from 36 to 18 chains. New results also indicate that cellulose interactions with xyloglucan are more limited than commonly believed, whereas pectin-cellulose interactions are more prevalent. Computational results indicate that xyloglucan binds tightest to the hydrophobic surface of cellulose microfibrils. Wall extensibility may be controlled at limited regions ("biomechanical hotspots") where cellulose-cellulose contacts are made, potentially mediated by trace amounts of xyloglucan.

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“…Before conducting SMD simulations, systems were equilibrated for 1.0 ns under an NVT ensemble at a temperature of T = 298 K. During equilibration, the positions of the carbon atoms in the leftmost fibril were constrained in the y-direction in order to prevent twisting of the fibrils (blue atoms in Figure 1E). Although cellulose fibrils tend to have an angle of twist of 1.5°/nm (Eichhorn and Davies, 2006;Zhao et al, 2013), the simulations aimed to limit this effect in order to decouple twisting effects from the interfacial separation and shear behavior.…”

Section: Steered Molecular Dynamics (Smd) Simulationsmentioning

confidence: 99%

Traction–separation laws and stick–slip shear phenomenon of interfaces between cellulose nanocrystals

Sinko

Keten

2015

Journal of the Mechanics and Physics of Solids

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Cellulose nanocrystals (CNCs) are one of nature's most abundant structural material building blocks and possess outstanding mechanical properties such as a tensile modulus comparable to Kevlar. It remains challenging to upscale these properties in CNC neat films and nanocomposites due to the difficulty of characterizing interfacial bonding between CNCs that govern stress transfer under deformation. Here we present new analyses based on atomistic simulations of shear and tensile failure of the interfaces between Iβ CNCs in elementary fibrils, providing new insight into factors governing the mechanical behavior of hierarchical nanocellulose materials. We compare the two most relevant crystal surfaces and find that hydrogen bonded surfaces have greater tensile strength compared to the surfaces governed by weaker interactions. On the contrary, shearing simulations show that friction between the atomic interfaces depends not only on surface energy but also the energy landscape along the shear direction. While being a weaker interface, the intersheet plane exhibits greater energy barriers to shear. The molecular roughness of this interface, characterized by a greater energy barrier, exhibits a stick-slip deformation behavior as opposed to a continuous sliding mechanism observed for the interfaces with hydrogen bonds. Analytical models to describe the energy landscapes are developed using energy scaling relations for van der Waals surfaces in combination with a modification of the Prandtl-Tomlinson model for atomic friction. Our simulations pave the way for tailoring hierarchical CNC materials by taking a similar approach to techniques employed for describing metals, where mechanical properties can be tuned through a deeper understanding of grain boundary physics and nanoscale interfaces. 3 Graphical Abstract: 4

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Cellulose Microfibril Twist, Mechanics, and Implication for Cellulose Biosynthesis

Cited by 88 publications

References 68 publications

Bacterial expansins and related proteins from the world of microbes

Bacterial expansins and related proteins from the world of microbes

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

Traction–separation laws and stick–slip shear phenomenon of interfaces between cellulose nanocrystals

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