Exo‐mode of action of cellobiohydrolase Cel48C from Paenibacillus sp. BP‐23

The enrichment from nature of novel microbial communities with high cellulolytic activity is useful in the identification of novel organisms and novel functions that enhance the fundamental understanding of microbial cellulose degradation. In this work we identify predominant organisms in three cellulolytic enrichment cultures with thermophilic compost as an inoculum. Community structure based on 16S rRNA gene clone libraries featured extensive representation of clostridia from cluster III, with minor representation of clostridial clusters I and XIV and a novel Lutispora species cluster. Our studies reveal different levels of 16S rRNA gene diversity, ranging from 3 to 18 operational taxonomic units (OTUs), as well as variability in community membership across the three enrichment cultures. By comparison, glycosyl hydrolase family 48 (GHF48) diversity analyses revealed a narrower breadth of novel clostridial genes associated with cultured and uncultured cellulose degraders. The novel GHF48 genes identified in this study were related to the novel clostridia Clostridium straminisolvens and Clostridium clariflavum, with one cluster sharing as little as 73% sequence similarity with the closest known relative. In all, 14 new GHF48 gene sequences were added to the known diversity of 35 genes from cultured species.The exploration and understanding of cellulose fermentation capabilities in nature could inform and enable industrial processes converting cellulosic biomass to fuels and other products. Enrichment of microbial communities that can utilize cellulose is useful in this context for the identification of novel organisms, novel metabolisms, and novel functions. Of particular interest are communities that can utilize cellulose at high temperatures and under anaerobic conditions, featuring high rates of solubilization under conditions where the energy and the reducing power of substrates are conserved in potentially useful fermentation products.Some evidence indicates that cocultures may be able to utilize cellulose more fully and produce higher concentrations of ethanol than pure cultures of model cellulolytic organisms such as Clostridium thermocellum and Clostridium straminisolvens (16,20,34). An initial step toward understanding the functional roles of community members in cooperative cellulose degradation is answering the question of what organisms are present in cellulolytic consortia obtained from nature. Currently, diversity estimation methods applied to cellulolytic communities range from traditional methods targeting the 16S rRNA gene (4, 12) to complex metagenomic analyses targeting the breadth of functional genes present in genomes of mixed cultures and the environment (3).From a functional gene standpoint, cellulase systems are complex assemblages of multifunctional glycosyl hydrolases. Even particularly relevant families, such as family 5 and family 9, tend to include hydrolases with multiple substrate specificities, deep evolutionary roots, and extensive sequence diversity within the same organism (19)...

Section: Discussionsupporting

confidence: 53%

Diversity of Bacteria and Glycosyl Hydrolase Family 48 Genes in Cellulolytic Consortia Enriched from Thermophilic Biocompost

Izquierdo

Sizova

Lynd

2010

“…The introduction of CBM3a into either Cel48F or Cel9G improved their activity on Avicel at the apparent expense of their activity on more tractable substrates, such as PAS-cellulose. Indeed, GH48 and GH9-CBM3c en- zymes appended with an efficient CBM3 (generally CBM3b) have been discovered in various bacteria (4,15,28,31). Acetivibrio cellulolyticus was also found to produce an enzymecontaining scaffolding protein that exhibits one GH9 module (not associated with a CBM3c), one CBM3b, and seven cohesin modules (8).…”

Section: Discussionmentioning

confidence: 99%

Exploration of New Geometries in Cellulosome-Like Chimeras

Mingardon

Chanal

Tardif

et al. 2007

In this study, novel cellulosome chimeras exhibiting atypical geometries and binding modes, wherein the targeting and proximity functions were directly incorporated as integral parts of the enzyme components, were designed. Two pivotal cellulosomal enzymes (family 48 and 9 cellulases) were thus appended with an efficient cellulose-binding module (CBM) and an optional cohesin and/or dockerin. Compared to the parental enzymes, the chimeric cellulases exhibited improved activity on crystalline cellulose as opposed to their reduced activity on amorphous cellulose. Nevertheless, the various complexes assembled using these engineered enzymes were somewhat less active on crystalline cellulose than the conventional designer cellulosomes containing the parental enzymes. The diminished activity appeared to reflect the number of protein-protein interactions within a given complex, which presumably impeded the mobility of their catalytic modules. The presence of numerous CBMs in a given complex, however, also reduced their performance. Furthermore, a "covalent cellulosome" that combines in a single polypeptide chain a CBM, together with family 48 and family 9 catalytic modules, also exhibited reduced activity. This study also revealed that the cohesin-dockerin interaction may be reversible under specific conditions. Taken together, the data demonstrate that cellulosome components can be used to generate higher-order functional composites and suggest that enzyme mobility is a critical parameter for cellulosome efficiency.

“…Exo-type cellulases (cellobiohydrolases) are divided into two groups: enzymes that recognize the reducing end (mainly belonging to families GH7 and GH48), and enzymes that recognize the nonreducing end (mainly belonging to GH6 and GH48) (34)(35)(36)(37). It has been reported that organisms that harbor both types of exo-type cellulases along with an endo-type enzyme, such as Thermomonospora fusca and Trichoderma reesei (34), display relatively high efficiency in cellulose degradation.…”

Section: Tc-chid(⌬s) or Tc-chid(⌬bd)mentioning

confidence: 99%

A Structurally Novel Chitinase from the Chitin-Degrading Hyperthermophilic Archaeon Thermococcus chitonophagus

Horiuchi

Aslam

Kanai

et al. 2016

A structurally novel chitinase, Tc-ChiD, was identified from the hyperthermophilic archaeon Thermococcus chitonophagus, which can grow on chitin as the sole organic carbon source. The gene encoding Tc-ChiD contains regions corresponding to a signal sequence, two chitin-binding domains, and a putative catalytic domain. This catalytic domain shows no similarity with previously characterized chitinases but resembles an uncharacterized protein found in the mesophilic anaerobic bacterium Clostridium botulinum. Two recombinant Tc-ChiD proteins were produced in Escherichia coli, one without the signal sequence [TcChiD(⌬S)] and the other corresponding only to the putative catalytic domain [Tc-ChiD(⌬BD)]. Enzyme assays using N-acetylglucosamine (GlcNAc) oligomers indicated that both proteins hydrolyze GlcNAc oligomers longer than (GlcNAc) 4 . Chitinase assays using colloidal chitin suggested that Tc-ChiD is an exo-type chitinase that releases (GlcNAc) 2 or (GlcNAc) 3 . Analysis with GlcNAc oligomers modified with p-nitrophenol suggested that Tc-ChiD recognizes the reducing end of chitin chains. While TcChiD(⌬BD) displayed a higher initial velocity than that of Tc-ChiD(⌬S), we found that the presence of the two chitin-binding domains significantly enhanced the thermostability of the catalytic domain. In T. chitonophagus, another chitinase ortholog that is similar to the Thermococcus kodakarensis chitinase ChiA is present and can degrade chitin from the nonreducing ends. Therefore, the presence of multiple chitinases in T. chitonophagus with different modes of cleavage may contribute to its unique ability to efficiently degrade chitin. IMPORTANCEA structurally novel chitinase, Tc-ChiD, was identified from Thermococcus chitonophagus, a hyperthermophilic archaeon. The protein contains a signal peptide for secretion, two chitin-binding domains, and a catalytic domain that shows no similarity with previously characterized chitinases. Tc-ChiD thus represents a new family of chitinases. Tc-ChiD is an exo-type chitinase that recognizes the reducing end of chitin chains and releases (GlcNAc) 2 or (GlcNAc) 3 . As a thermostable chitinase that recognizes the reducing end of chitin chains was not previously known, Tc-ChiD may be useful in a wide range of enzyme-based technologies to degrade and utilize chitin. Chitin is a ␤-1,4-linked insoluble linear polymer of N-acetylglucosamine (GlcNAc) and is the main component of the exoskeleton of crustaceans and insects, as well as the cell walls of fungi. Chitin is the second most abundant natural polysaccharide after cellulose, and its annual formation rate is in the order of 10 10 to 10 11 tons (1). At present, the majority of chitin remains unused, and thus the development of effective methods to convert chitin into useful biomaterials and/or bioenergy is important to maintain our supplies of edible polysaccharides, such as starch.Chitinases are enzymes responsible for the hydrolysis of chitin polymer, and they produce GlcNAc and/or its oligomers as products. Chitinases are found ...