Extraction of cellulose-synthesizing activity of Gluconacetobacter xylinus by alkylmaltoside

The BcsD subunit of type I bacterial cellulose synthase interacts dynamically with the BcsAB catalytic core complex

Cellulose synthase has two distinct functions: synthesis of the cellulose molecule (polymerization) and assembling the synthesized cellulose chains into the crystalline microfibril (crystallization). In the type I bacterial cellulose synthase (Bcs) complex, four major subunits - BcsA, BcsB, BcsC and BcsD - work in a coordinated manner. This study showed that the crystallization subunit BcsD interacts with the polymerization complex BcsAB in two modes: direct protein-protein interactions and indirect interactions through the product cellulose. We hypothesized that the former and latter modes represent the basal and active states of type I bacterial cellulose synthase, respectively, and this dynamic behaviour of the BcsD protein regulates the crystallization process of cellulose chains.

Observation of in vitro cellulose synthesis by bacterial cellulose synthase with time-resolved small angle X-ray scattering

Cellulose synthase is the enzyme that produces cellulose in the living organisms like plant, and has two functions: polymerizing glucose residues (polymerization) and assembling these polymerized molecules into a crystalline microfibril with a "cellulose I" crystallographic structure (crystallization). Many studies, however, have shown that an in vitro reaction of cellulose synthase produces aggregates of a non-native crystallographic structure "cellulose II", despite the remaining polymerizing activity. This is partial denaturation or loss of crystallization function in cellulose synthase, which needs to be resolved to reconstitute its native activity. To this end, we aimed to clarify the process of cellulose II formation by bacterial cellulose synthase in vitro, using in situ small angle X-ray scattering (SAXS). An increase in scattering specific to synthesis was observed around two distinct regions of q (0.2-0.4 nm^-1 and <0.1 nm^-1) by time-resolved SAXS measurement. The scattering at higher q-region appears prior to lower-q scattering at beginning of the reaction, indicating the existence of smaller primitive aggregations at the initiation stage. This study demonstrates the use of in situ SAXS measurement to decipher the dynamics of biosynthesized cellulose chains, which is a remarkable example of polymer assembly in ambient conditions.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: An update for 2011-2012

This review is the seventh update of the original article published in 1999 on the application of MALDI mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2012. General aspects such as theory of the MALDI process, matrices, derivatization, MALDI imaging, and fragmentation are covered in the first part of the review and applications to various structural types constitute the remainder. The main groups of compound are oligo- and poly-saccharides, glycoproteins, glycolipids, glycosides, and biopharmaceuticals. Much of this material is presented in tabular form. Also discussed are medical and industrial applications of the technique, studies of enzyme reactions, and applications to chemical synthesis. © 2015 Wiley Periodicals, Inc. Mass Spec Rev 36:255-422, 2017.

AcsA-AcsB: The core of the cellulose synthase complex from Gluconacetobacter hansenii ATCC23769

The gram-negative bacterium, Gluconacetobacter hansenii, produces cellulose of exceptionally high crystallinity in comparison to the cellulose of higher plants. This bacterial cellulose is synthesized and extruded into the extracellular medium by the cellulose synthase complex (CSC). The catalytic component of this complex is encoded by the gene AcsAB. However, several other genes are known to encode proteins critical to cellulose synthesis and are likely components of the bacterial CSC. We have purified an active heterodimer AcsA-AcsB from G. hansenii ATCC23769 to homogeneity by two different methods. With the purified protein, we have determined how it is post-translationally processed, forming the active heterodimer AcsA-AcsB. Additionally, we have performed steady-state kinetic studies on the AcsA-AcsB complex. Finally through mutagenesis studies, we have explored the roles of the postulated CSC proteins AcsC, AcsD, and CcpAx.

Functional reconstitution of cellulose synthase in Escherichia coli

Cellulose is a high molecular weight polysaccharide of β1 → 4-d-glucan widely distributed in nature-from plant cell walls to extracellular polysaccharide in bacteria. Cellulose synthase, together with other auxiliary subunit(s) in the cell membrane, facilitates the fibrillar assembly of cellulose polymer chains into a microfibril. The gene encoding the catalytic subunit of cellulose synthase is cesA and has been identified in many cellulose-producing organisms. Very few studies, however, have shown that recombinant CesA protein synthesizes cellulose polymer, but the mechanism by which CesA protein synthesizes cellulose microfibrils is not known. Here we show that cellulose-synthesizing activity is successfully reconstituted in Escherichia coli by expressing the bacterial cellulose synthase complex of Gluconacetobacter xylinus: CesA and CesB (formerly BcsA and BcsB, respectively). Cellulose synthase activity was, however, only detected when CesA and CesB were coexpressed with diguanyl cyclase (DGC), which synthesizes cyclic-di-GMP (c-di-GMP), which in turn activates cellulose-synthesizing activity in bacteria. Direct observation by electron microscopy revealed extremely thin fibrillar structures outside E. coli cells, which were removed by cellulase treatment. This fiber structure is not likely to be the native crystallographic form of cellulose I, given that it was converted to cellulose II by a chemical treatment milder than ever described. We thus putatively conclude that this fine fiber is an unprecedented structure of cellulose. Despite the inability of the recombinant enzyme to synthesize the native structure of cellulose, the system described in this study, named "CESEC (CEllulose-Synthesizing E. Coli)", represents a useful tool for functional analyses of cellulose synthase and for seeding new nanomaterials.

Degradation and synthesis of β-glucans by a Magnaporthe oryzae endotransglucosylase, a member of the glycoside hydrolase 7 family

BACKGROUND

Plant pathogens secrete enzymes that degrade plant cell walls to enhance infection and nutrient acquisition.

RESULTS

A novel endotransglucosylase catalyzes cleavage and transfer of β-glucans and decreases the physical strength of plant cell walls.

CONCLUSION

Endotransglucosylation causes depolymerization and polymerization of β-glucans, depending on substrate molecular size.

SIGNIFICANCE

Enzymatic degradation of plant cell walls is required for wall loosening, which enhances pathogen invasion. A Magnaporthe oryzae enzyme, which was encoded by the Mocel7B gene, was predicted to act on 1,3-1,4-β-glucan degradation and transglycosylation reaction of cellotriose after partial purification from a culture filtrate of M. oryzae cells, followed by liquid chromatography-tandem mass spectrometry. A recombinant MoCel7B prepared by overexpression in M. oryzae exhibited endo-typical depolymerization of polysaccharides containing β-1,4-linkages, in which 1,3-1,4-β-glucan was the best substrate. When cellooligosaccharides were used as the substrate, the recombinant enzyme generated reaction products with both shorter and longer chain lengths than the substrate. In addition, incorporation of glucose and various oligosaccharides including sulforhodamine-conjugated cellobiose, laminarioligosaccharides, gentiobiose, xylobiose, mannobiose, and xyloglucan nonasaccharide into β-1,4-linked glucans were observed after incubation with the enzyme. These results indicate that the recombinant enzyme acts as an endotransglucosylase (ETG) that cleaves the glycosidic bond of β-1,4-glucan as a donor substrate and transfers the cleaved glucan chain to another molecule functioning as an acceptor substrate. Furthermore, ETG treatment caused greater extension of heat-treated wheat coleoptiles. The result suggests that ETG functions to induce wall loosening by cleaving the 1,3-1,4-β-glucan tethers of plant cell walls. On the other hand, use of cellohexaose as a substrate for ETG resulted in the production of cellulose II with a maximum length (degree of polymerization) of 26 glucose units. Thus, ETG functions to depolymerize and polymerize β-glucans, depending on the size of the acceptor substrate.

Synthase-dependent exopolysaccharide secretion in Gram-negative bacteria

The biosynthesis and export of bacterial cell-surface polysaccharides is known to occur through several distinct mechanisms. Recent advances in the biochemistry and structural biology of several proteins in synthase-dependent polysaccharide secretion systems have identified key conserved components of this pathway in Gram-negative bacteria. These components include an inner-membrane-embedded polysaccharide synthase, a periplasmic tetratricopeptide repeat (TPR)-containing scaffold protein, and an outer-membrane β-barrel porin. There is also increasing evidence that many synthase-dependent systems are post-translationally regulated by the bacterial second messenger bis-(3'-5')-cyclic dimeric guanosine monophosphate (c-di-GMP). Here, we compare these core proteins in the context of the alginate, cellulose, and poly-β-D-N-acetylglucosamine (PNAG) secretion systems.