Editing Cellulase (section)

=== Cellulase complexes ===

In many bacteria, cellulases in vivo are complex enzyme structures organized in [[Supramolecular assembly|supramolecular complexes]], the [[cellulosomes]]. They can contain, but are not limited to, five different enzymatic subunits representing namely endocellulases, exocellulases, cellobiases, oxidative cellulases and cellulose phosphorylases wherein only exocellulases and cellobiases participate in the actual hydrolysis of the β(1→4) linkage. The number of sub-units making up cellulosomes can also determine the rate of enzyme activity.<ref>{{cite journal | vauthors = Tsai SL, DaSilva NA, Chen W | title = Functional display of complex cellulosomes on the yeast surface via adaptive assembly | journal = ACS Synthetic Biology | volume = 2 | issue = 1 | pages = 14–21 | date = January 2013 | pmid = 23656322 | doi = 10.1021/sb300047u | citeseerx = 10.1.1.701.5515 }}</ref>

Multidomain cellulases are widespread among many taxonomic groups, however, cellulases from anaerobic bacteria, found in cellulosomes, have the most complex architecture consisting of different types of modules. For example, ''Clostridium cellulolyticum'' produces 13 GH9 modular cellulases containing a different number and arrangement of catalytic-domain (CD), carbohydrate-binding module (CBM), dockerin, linker and Ig-like domain.<ref name="pmid24451379">{{cite journal | vauthors = Ravachol J, Borne R, Tardif C, de Philip P, Fierobe HP | title = Characterization of all family-9 glycoside hydrolases synthesized by the cellulosome-producing bacterium ''Clostridium cellulolyticum'' | journal = The Journal of Biological Chemistry | volume = 289 | issue = 11 | pages = 7335–48 | date = March 2014 | pmid = 24451379 | pmc = 3953250 | doi = 10.1074/jbc.M113.545046 | doi-access = free }}</ref>

The cellulase complex from ''[[Trichoderma reesei]]'', for example, comprises a component labeled C1 (57,000 [[dalton (unit)|dalton]]s) that separates the chains of crystalline cellulose, an endoglucanase (about 52,000 daltons), an exoglucanase (about 61,000 dalton), and a β-glucosidase (76,000 daltons).<ref name=worth>Worthington Biochemical Corporation (2014), [http://www.worthington-biochem.com/cel/default.html Cellulase]. Accessed on 2014-07-03</ref>

Numerous "signature" sequences known as [[dockerin]]s and [[cohesin]]s have been identified in the [[genome]]s of bacteria that produce cellulosomes. Depending on their [[amino acid sequence]] and [[tertiary structures]], cellulases are divided into clans and families.<ref name="pmid9818257">{{cite journal | vauthors = Bayer EA, Chanzy H, Lamed R, Shoham Y | title = Cellulose, cellulases and cellulosomes | journal = Current Opinion in Structural Biology | volume = 8 | issue = 5 | pages = 548–57 | date = October 1998 | pmid = 9818257 | doi = 10.1016/S0959-440X(98)80143-7 }}</ref>

Multimodular cellulases are more efficient than free enzyme (with only CD) due to synergism because of the close proximity between the enzyme and the cellulosic substrate. CBM are involved in binding of cellulose whereas glycosylated linkers provide flexibility to the CD for higher activity and protease protection, as well as increased binding to the cellulose surface.<ref name="guerriero" />