Cellulosome

Murashima, K., Chen, C.-L., Kosugi, A. et al. (2002) Heterologous production of Clostridium cellulovorans engB, using protease-deficient Bacillus subtilis, and preparation of active recombinant cellulosomes. Journal of Bacteriology, 184 (1), 76-81. 

Within the cellulosome complex, type I dockerin domain is responsible for incorporating its associated glycosyl hydrolase in the bacterial cellulosome via interaction with a reception domain, the cohesin domain. The three-dimensional solution structure of the 69-residue dockerin domain from the thermophilic Clostridium thermocellum (Topt = 55-65 °C) was solved by NMR and was found to consist of two Ca " -binding loop-helix motifs connected by a linker. Each Ca " -binding subdomain is stabilized by a cluster of buried hydrophobic sidechains. Recently, the NMR sequence-specific resonance assignment of type II cohesin module from C. thermocellum has been published. ... 

The work to be summarized here is preliminary and will be published elsewhere (manuscripts in preparation). Thermoanaerobacter strain B6A produces a xylanase complex diat is inducible by xylose and catabolite repressed by glucose. Noticeably, when mixed with insoluble xylan, glucose-grown cells do not bind xylan whereas, xylose-grown cells bind very tightly. Canonized ferritin was used to identify xylanosome structures in xylose grown cells which are similar to cellulosomes observed in C. thermocellum, Thermoanaerobacter strain B6A produces thermostable cell-bound endoxylanase, which is also excreted. 

Bayer, E. A., E. Morag, Y. Shoham, J. Tormo, and R. Lamed. 1996. The cellulosome A cell surface organelle for the adhesion to and degradation of cellulose. In Bacterial Adhesion Molecular and Ecological Diversity (M. Fletcher, Ed.), Wiley Series in Ecological and Applied Microbiology pp. 155-182. Wiley-Liss, New York. 

Schwarz W. H. (2001) The cellulosome and cellulose degradation by anaerobic bacteria. Appl. Microbiol. Bio-technol. 56(5-6), 634-649. 

After catalytic domains, the next most common domains are CBDs which are usually j oined to the catalytic domain by a short tinker peptide. Cellulases that are present in cellulosomes contain short domains called dockerins that bind to specific sites on a scaffoldin protein to form a cellulosome [30]. A number of cellulases contain fibronectin-like domains, but the function of these domains is not known [6]. There are several other domains with unknown functions [6]. 

A key component of cellulosomes is a 200,000 MW protein, scaffoldin, that contains at least nine copies of a cohesin domain, a family Ilia cellulose-binding domain, and a dockerin-like domain that appears to bind scaffoldin to the cell surface. The cohesin domains are the binding sites for the dockerin domains that are present at the C-terminus of each cellulase molecule present in the cellulosome. At this time, it appears that all the cohesin domains of a given species bind with nearly equal affinity to the dockerin domains present on the cellulo-somal enzymes of that species [92]. This result suggests that cellulosomes are a... 

There does not appear to be a special class of cellulases in cellulosomes since most of the cellulosomal hydrolases belong to the same set of families as those... 

White BA, Cann IKO, Mackie RI, Morrison M (1997) Cellulase and xylanase genes from ruminal bacteria domain analysis suggests a non-cellulosome-like model for organization of the cellulase complex. In Onodera R, Itabashi H, Ushida K, Yano H,Sasaki Y (eds) Rumen microbes and digestive physiology in ruminants. Jpn Sci Soc Press, Tokyo, p 69... 

Morag E, Yaron S, Lamed R, Kenig R, Shoham Y, Bayer EA (1996) J Biotechnol 51 235 Bayer EA, Morag E, Shoham Y, Tormo J, Lamed R (1996) The cellulosome a cell surface organelle for the adhesion to and degradation of cellulose. In Fletcher M (ed) Bacterial adhesion molecular and ecological diversity. Wiley, New York, p 155... 

CE Family 1 is very large and contains members which do not act on carbohydrate-derived substrates. The crystal structure of a CE 1 domain of XynlOB modular enzyme from Clostridium thermocellum has been solved. " The CE 1 domain is a feruloyl esterase which hydrolyses the feruloyl groups attached to some arabinofuranosyl 05 groups in native xylan. (The Xyn lOB protein as a whole consists of two CBM 22 domains, a dockerin domain, and a GH 20 xylanase domain, and forms part of a cellulosome - see Section 5.10.) The enzyme has the common a/p hydrolase fold. Studies of ferulic acid complexes of the inactive alanine mutant of the active site serine revealed the classic catalytic triad, and two main-chain peptide NH bonds are in place to form an oxyanion hole . A remarkable feature is that the enzyme as repeatedly isolated was esterilied on the active site serine by phosphate or sulfate. 

Structure and Synergistic Effect of Cellulases 11.4.3.6.1 The Cellulosome Concept... 

The enzymatic hydrolysis of intractable cellulosic and hemicellulosic substrates of the plant cell-wall is efficiently performed by multienzyme machines designated under the collective name of cellulosomes. Cellulosomes are large extracellular enzyme... 

E. A. Bayer, J.-P. Belaich, Y. Shoham, and R. Lamed, The cellulosomes Multienzyme machines for degradation of plant cell wall polysaccharides, Annu. Rev. Microbiol, 58 (2004) 521-524. 

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