2010-05-26T06:47:55Z

Bareket Dassa:

{{UnderConstruction}}
* [[Author]]s: ^^^Orly Alber^^^, ^^^Bareket Dassa^^^, and ^^^Ed Bayer^^^
* [[Responsible Curator]]: ^^^Ed Bayer^^^
----

== Cellulosome complex ==
Cellulosome complexes are intricate multi-enzyme machines produced by many cellulolytic microorganisms. They are designed for efficient degradation of plant cell wall polysaccharides, notably cellulose — the most abundant organic polymer on Earth. The cellulosome consists of a multi-functional integrating subunit (called scaffoldin), responsible for organizing the various cellulolytic subunits (e.g., the enzymes) into the complex. Within a cellulosome, multiple endoglucanases, cellobiohydrolases, xylanases and other degradative enzymes work synergistically to attack heterogeneous, insoluble cellulose substrates. This is accomplished by the interaction of two complementary classes of module, located on the two separate types of interacting subunits, i.e., a cohesin module on the scaffoldin and a dockerin module on each enzymatic subunit. The high-affinity cohesin-dockerin interaction defines the cellulosome structure. Attachment of the cellulosome to its substrate is mediated by a scaffoldin-borne cellulose-binding module (CBM) that comprises part of the scaffoldin subunit. Much of our understanding of its catalytic components, architecture, and mechanisms of attachment to the bacterial cell and to cellulose, has been derived from the study of ''Clostridium thermocellum''.
[[File:Cellulosome.jpg|500px|thumb|Architecture of the ''C. thermocellum'' cellulosome system]]
'''Cellulosome components:'''
* '''The scaffoldin subunit''' contains one or more cohesin modules connected to other types of functional modules. In a given scaffoldin, the latter types of modules may include a cellulose-specific carbohydrate-binding module (CBM), a dockerin, X modules of unknown function, an S-layer homology (SLH) module or a sortase anchoring motif.

* '''Cohesin modules''' are the major building blocks of scaffoldins, which are responsible for organizing the cellulolytic subunits into the multi-enzyme complex.

* '''Dockerin modules''' anchor the catalytic enzymes to the scaffoldin. The dockerin displays internal two-fold symmetry, consisting of a duplicated F-hand motif (a calcium-binding loop preceding an a helix). The dockerin can also be found in the C- terminus of scaffoldins.

* '''Catalytic subunits''' contain dockerin modules that serve to incorporate catalytic modules into the cellulosome complex. These catalytic modules include: glycoside hydrolases, polysaccharide lyases, and carboxyl esterases [http://www.weizmann.ac.il/Biological_Chemistry/scientist/Bayer/new_pages/reserch_topics/enzymes.html].

=== Cellulosome systems ===
Bacterial cellulosomal systems can be categorized into two major types: simple cellulosome systems contain a single scaffoldin and complex cellulosome systems exhibit multiple types of interacting scaffoldins. The arrangement of the modules on the scaffoldin subunit and the specificity of the cohesin(s) and/or dockerin for their modular counterpart dictate the overall architecture of the cellulosome. Several different types of scaffoldins have been described: the primary scaffoldins incorporate the various dockerin-bearing subunits directly into the cellulosome complex, adaptor scaffoldins increase the repertoire or number of components into the complex, and the anchoring scaffoldins attach the complex to the bacterial cell surface.

'''Currently known cellulosome-producing anaerobic bacteria:'''
* ''Acetivibrio cellulolyticus''
* ''Bacteroides cellulosolvens''
* ''Clostridium acetobutylicum''
* ''Clostridium cellobioparum''
* ''Clostridium cellulolyticum''
* ''Clostridium cellulovorans''
* ''Clostridium josui''
* ''Clostridium papyrosolvens''
* ''Clostridium thermocellum''
* ''Ruminococcus albus''
* ''Ruminococcus flavifaciens''

Cellulosomes exist as extracellular complexes that are either attached to the cell wall of bacteria or free in solution, where the insoluble substrate can be broken down into soluble products and taken up by the cell. The large size and heterogeneity of cellulosomes from the best-characterized organisms (i.e., ''C. thermocellum'', ''C. cellulolyticum'', and ''C. cellulovorans'') have greatly complicated efforts to probe cellulosome structure and function. Other cellulosome systems (such as those from ''Acetivibrio cellulolyticus'' and ''Ruminococcus flavefaciens'') appear to be even more intricate.

The genes encoding for many important cellulosome subunits are organized in “enzyme-linked gene clusters” on the chromosome.

'''Simple Cellulosome Systems'''

In the simple cellulosome systems, the scaffoldins contain a single CBM, one or more X2 modules and numerous (5 to 9) cohesins. These scaffoldins are primary scaffoldins, which incorporate the dockerin-bearing enzymes into the complex. In several cases, the simple cellulosomes have been shown to be associated with the cell surface, but the molecular mechanism responsible for this is still unclear. The X2 module may play a role in attachment to the cell wall.

'''Complex Cellulosome Systems'''

To date, complex cellulosome systems have been described in different bacterial species ([http://www.weizmann.ac.il/Biological_Chemistry/scientist/Bayer/new_pages/reserch_topics/cellulosome_systems.html]). In these systems, more than one scaffoldin interlocks with each other in various ways to produce a complex cellulosome architecture. At least one type of scaffoldin serves as a primary scaffoldin that incorporates the enzymes directly into the cellulosome complex. In each species, another type of scaffoldin attaches the cellulosome complex to the cell surface via a specialized module or sequence, designed for this purpose.
[[File:Clostridium_cellulosome.jpg|500px|thumb|Schematic representation of ''C. thermocellum'' cellulosome components]]

== Cohesin-dockerin interactions ==
'''Cohesin-dockerin interactions''' can be viewed as a kind of plug-and-socket mechanism in which the dockerin plugs into the cohesin socket1. In general, the interaction is inter-species and intra-species (type) specific, although some cross-reactivity has been found in a few cases. The cohesin-dockerin interaction is one of the most potent protein-protein interactions known in nature, in most cases approaching the strength of high-affinity antigen-antibody interactions (Ka ~ 1011 M-1).

So far, cohesins have been phylogenetically distributed into three groups according to sequence homology; the type-I cohesin, the type-II cohesin and the recently discovered type-III cohesin. The dockerins that interact with each cohesin type are, by definition, of the same type.

== Structural characterization of cellulosome components ==
One of the greatest efforts in the cellulosome research field is to understand the structure-function relationship in cellulosome assembly. Thus far, the crystallographic structure of only selected cohesins has been determined, including three different type-I cohesins, all of which share the typical jelly-roll topology that forms a flattened 9-stranded beta-sandwich. The structures of several type-II cohesins have also been determined. The type-II and type-III cohesins has the same jelly-roll topology as the type-I cohesins with several additional structural elements: an alpha-helix at the crown of the molecule (located in the loop connecting strands 6-7, and 8-9 for type-II and type-III, respectively), and two “beta-flaps” that provisionally disrupt the normal course of beta-strands 4 and 8.
[[File:Cohesin_complex.jpg|500px|thumb|Crystal structures of type-I, II and III cohesin modules]]

== History of discovery ==
In the early 1980s, Profs. Raffi Lamed and Ed Bayer met at Tel Aviv University and commenced their work that led to the discovery of the cellulosome concept.

At the time, they weren’t looking for enzymes or cellulosomes at all. They simply sought a ‘cellulose-binding factor’ or ‘CBF’ on the cell surface of the anaerobic thermophilic bacterium, ''Clostridium thermocellum,'' which they inferred would account for the observation that the bacterium attaches strongly to the insoluble cellulose substrate prior to its degradation. They employed a then unconventional experimental approach, in which they isolated an adherence-defective mutant of the bacterium and prepared a specific polyclonal antibody for detection of the functional component. Surprisingly, they isolated a very large multi-subunit supramolecular complex, instead of a small protein. A combination of biochemical, biophysical, immunochemical and ultrastructural techniques, followed by molecular biological verification, led to the definition and proof of the cellulosome concept. The birth of the discrete, multi-enzyme cellulosome complex was thus documented.

== References ==
For further information, visit Prof. Ed Bayer's page [http://www.weizmann.ac.il/Biological_Chemistry/scientist/Bayer/index.html].
<biblio>
#cellulosome1 pmid=15487947
#cellulosome2 pmid=20373916
#cellulosome3 pmid=19107866
#cellulosome4 pmid=17367380
#cellulosome5 pmid=15197390
#cellulosome6 pmid=15755956
</biblio>

[[Category:Definitions and explanations]]

File:Cohesin complex.jpg

2010-05-26T06:47:25Z

Bareket Dassa:

User:Bareket Dassa

2010-05-26T06:44:35Z

Bareket Dassa:

[[Image:Bareket_Dassa.jpg|left|]]
Dr. Bareket Dassa is a Post Doctoral Fellow at [http://www.weizmann.ac.il/Biological_Chemistry/scientist/Bayer/ Ed Bayer’s] lab, in the Department of [http://www.weizmann.ac.il/Biological_Chemistry/ Biological Chemistry] at the [http://www.weizmann.ac.il Weizmann Institute of Science], Rehovot, Israel. She is applying bioinformatic approaches to explore the diversity and evolution of [http://www.weizmann.ac.il/Biological_Chemistry/scientist/Bayer/new_pages/reserch_topics/cellulosome_systems.html cellulosomes] in different cellulolytic bacteria. Her contibution to CAZypedia was editing the [[GH48]] and the cellulosome pages.

Bareket was awarded her Master’s and Ph.D Degrees from the Weizmann Institute of Science under the supervision of Prof. [http://bioinformatics.weizmann.ac.il/~pietro/ Shmuel Pietrokovski], studying the sequence and function of [http://bioinformatics.weizmann.ac.il/~pietro/inteins/ inteins]and bacterial [http://bioinformatics.weizmann.ac.il/~pietro/BILs/ protein-splicing domains].

email: bareket.dassa at weizmann.ac.il

[http://www.weizmann.ac.il/Biological_Chemistry/scientist/Bayer/new_pages/members/Bareket_CV.html Publications]

[[Category:Contributors|Dassa, Bareket]]

File:Cohesinstr.jpg

2010-05-26T06:42:30Z

Bareket Dassa: uploaded a new version of "File:Cohesinstr.jpg"

2010-04-14T10:49:58Z

Bareket Dassa:

{{CuratorApproved}}
* [[Author]]: ^^^Bareket Dassa^^^
* [[Responsible Curator]]: ^^^Ed Bayer^^^
----


<div style="float:right">
{| {{Prettytable}}
|-
|{{Hl2}} colspan="2" align="center" |'''Glycoside Hydrolase Family GH48'''
|-
|'''Clan'''
|GH-M
|-
|'''Mechanism'''
|inverting
|-
|'''Active site residues'''
|Proton donor: known; Nucleophile: unknown
|-
|{{Hl2}} colspan="2" align="center" |'''CAZy DB link'''
|-
| colspan="2" |http://www.cazy.org/fam/GH48.html
|}
</div>


== Substrate specificities ==
'''Family 48''' [[glycoside hydrolases]] are major and key components of some cellulase systems, occurring in free enzyme systems (e.g., in ''[http://www.cazy.org/b291.html Thermobifida fusca]''), multi-functional enzymes (e.g, in ''[http://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?id=44001 Caldicellulosiruptor saccharolyticus]''), anaerobic fungi (e.g., ''[http://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?id=99929 Piromyces equi]'') and every [http://www.weizmann.ac.il/Biological_Chemistry/scientist/Bayer/new_pages/reserch_topics/cellulosome_systems.html cellulosome] system thus far described. The GH48 cellulase is commonly the most abundant enzyme subunit in cellulosome-producing bacteria. Each bacterium usually contains a single gene that codes for a GH48 enzyme, although a few bacteria (e.g., ''[http://www.cazy.org/b514.html Clostridium thermocellum]'' and ''[http://www.cazy.org/b897.html Anaerocellum thermophilum]'') contain two or more GH48 genes. Of the two ''C. thermocellum'' GH48 enzymes, one (Cel48S) is a [http://www.weizmann.ac.il/Biological_Chemistry/scientist/Bayer/new_pages/reserch_topics/Cohesin_dockerin.html dockerin]-containing cellulosomal enzyme, and the other (Cel48Y) is a free, non-cellulosomal enzyme that contains a cellulose-binding CBM3.

The following activities have been reported: endo-β-1,4-glucanase, chitinase, endo-processive cellulase and cellobiohydrolase. Its preferred substrate is amorphous or crystalline cellulose over carboxymethylcellulose (CMC), and its activity is strongly inhibited by the presence of cellobiose. Although its activity on various substrates is characteristically very low, it is thought to be a critically important enzyme which imparts a major component of synergy to its cellulase system.

== Kinetics and Mechanism ==
The glycoside hydrolases of this family are [[inverting]] glycosidases, which preferentially attack the reducing end of the substrate <cite>Barr1996</cite>.

The native and recombinant Cel48S from ''C. thermocellum'' displays typical characteristics of a processive exoglucanase <cite>Beatriz2002</cite>, and its activity on amorphous cellulose is optimal at 70 °C and at pH 5–6.

Family 48 cellulases (i.e., CelS/S8 from ''C. thermocellum'', Avicelase II of ''C. stercorarium'') are stabilized at high temperatures by Ca2+ or other bivalent ions <cite>Bronnenmeier1991, Morag1991, Kruus1995</cite>.

The Cel48F protein from ''C. cellulolyticum'' has been reported <cite>Reverbel-Leroy1997</cite> to be a processive [[endo]]-glucanase, which performs a processive degradation of the cellulose chain after an initial endo-attack. A two-step mechanism was proposed <cite>Parsiegla2008</cite>, in which processive action and chain disruption occupy different subsites.

== Catalytic Residues ==
The crystal structure of Cel48F, a cellulosome component of ''C. cellulolyticum'', revealed the active center at the junction of the cleft and tunnel regions, where Glu55 is the proposed proton donor in the cleavage reaction, and the corresponding base was initially proposed to be either Glu44 or Asp230 <cite>Parsiegla1998</cite>.

The structure of the catalytic module of Cel48S of ''C. thermocellum'' showed a similar tunnel-shaped substrate-binding region formed by the alpha helices in the protein. The hydrolysis of the cellulose chain in Cel48S appeared to involve Glu87 (the equivalent of Glu55 in ''C. cellulolyticum'' Cel48F) as an acid to protonate the glycosidic oxygen atom and Tyr351 as a base to extract a proton from the nucleophilic water molecule that attacks the anomeric carbon atom.

More recent studies of Cel48F failed to unambiguously identity the catalytic base in the cleavage reaction <cite>Parsiegla2008</cite>.

== Three-dimensional structures ==
Three-dimensional structures are available for two family 48 enzymes: Cel48F (from ''Clostridium cellulolyticum'') and Cel48A (from ''Clostridium thermocellum''). Both enzymes have an (α/α)6 barrel topology.
<gallery widths=200px heights=220px perrow=2 caption="3D structures of GH48 proteins (click images for large versions)">
File:1FAE.jpg|PDB ID [{{PDBlink}}1fae 1fae] from "Crystal structure of the cellulase CEL48F from ''C. cellulolyticum'' in complex with cellobiose" <cite>Parsiegla2000</cite>.
File:1L1Y.jpg|PDB ID [{{PDBlink}}1l1y 1l1y] and [{{PDBlink}}1L2A 1L2A] from "The Crystal Structure and Catalytic Mechanism of Cellobiohydrolase CelS, the Major Enzymatic Component of the ''Clostridium thermocellum'' cellulosome" <cite>Guimaraes2002</cite>, in complex with cellohexaose and cellobiose.
</gallery>
3D structures of Cel48F in complex with different ligands are also available:
* with cellotetraose ([{{PDBlink}}1f9d 1f9d])
* with the thio-oligosaccharide inhibitor PIPS-IG3 ([{{PDBlink}}1f9o 1f9o])
* with cellobiose ([{{PDBlink}}1fea 1fae])
* with cellobiitol ([{{PDBlink}}1fbo 1fbo])
* with cellohexaose ([{{PDBlink}}1fbw 1fbw])
* with a thio-oligosaccharide ([{{PDBlink}}1g9j 1g9j])
* mutant E55Q with a thio-oligosaccharide ([{{PDBlink}}2qno 2qno])
== Family Firsts ==
;First sterochemistry determination: ''Cellulomonas fimi'' CenE, described as an endo-β-1,4-glucanase, catalyzes the hydrolysis of cellohexaose with inversion of anomeric carbon configuration, characteristic of a single displacement reaction <cite>Shen1994 </cite>.

;First [[catalytic nucleophile]] identification: …“Waiting patiently”… (see <cite>Parsiegla2008</cite>).

;First [[general acid/base]] residue identification: Glu was the proposed proton donor in the cleavage reaction <cite>Parsiegla1998</cite>.

;First 3-D structure: The crystal structure of catalytic module of ''C. cellulolyticum'' Cel48F in complex with oligosaccharides <cite>Parsiegla2008</cite>.

;First cloning and sequencing: The ''cel48S'' gene from ''C. thermocellum'' <cite>Wang1993 </cite>.

== References ==
<biblio>
#Barr1996 pmid=8555231
#Beatriz2002 pmid=12096911
#Bronnenmeier1991 pmid=1909625
#Morag1991 pmid=2061292
#Kruus1995 pmid=7883725
#Reverbel-Leroy1997 pmid=8981979
#Parsiegla2008 pmid=18035374
#Parsiegla1998 pmid=9755156
#Parsiegla2000 pmid=10985769
#Guimaraes2002 pmid=12096911
#Shen1994 pmid=8147863
#Wang1993 pmid=8444792
#Steenbakkers2002 pmid=12652902
#Zverlov1998 pmid=9493383
#Fujita2006 pmid=16684504
#Xu2004 pmid=14761991
#Devillard2004 pmid=14679233
#Sanchez2003 pmid=12823562
#Irwin2000 pmid=10931180
</biblio>

[[Category:Glycoside Hydrolase Families|GH048]]

Cellulosome

2010-04-13T11:36:04Z

Bareket Dassa:

{{UnderConstruction}}
* [[Author]]s: ^^^Orly Alber^^^, ^^^Bareket Dassa^^^, and ^^^Ed Bayer^^^
* [[Responsible Curator]]: ^^^Ed Bayer^^^
----

== Cellulosome complex ==
Cellulosome complexes are intricate multi-enzyme machines produced by many cellulolytic microorganisms. They are designed for efficient degradation of plant cell wall polysaccharides, notably cellulose — the most abundant organic polymer on Earth. The cellulosome consists of a multi-functional integrating subunit (called scaffoldin), responsible for organizing the various cellulolytic subunits (e.g., the enzymes) into the complex. Within a cellulosome, multiple endoglucanases, cellobiohydrolases, xylanases and other degradative enzymes work synergistically to attack heterogeneous, insoluble cellulose substrates. This is accomplished by the interaction of two complementary classes of module, located on the two separate types of interacting subunits, i.e., a cohesin module on the scaffoldin and a dockerin module on each enzymatic subunit. The high-affinity cohesin-dockerin interaction defines the cellulosome structure. Attachment of the cellulosome to its substrate is mediated by a scaffoldin-borne cellulose-binding module (CBM) that comprises part of the scaffoldin subunit. Much of our understanding of its catalytic components, architecture, and mechanisms of attachment to the bacterial cell and to cellulose, has been derived from the study of Clostridium thermocellum.
[[File:Cellulosome.jpg|500px|thumb|alt text]]
'''Cellulosome components:'''
* '''The scaffoldin subunit''' contains one or more cohesin modules connected to other types of functional modules. In a given scaffoldin, the latter types of modules may include a cellulose-specific carbohydrate-binding module (CBM), a dockerin, X modules of unknown function, an S-layer homology (SLH) module or a sortase anchoring motif. The arrangement of the modules on the scaffoldin subunit and the specificity of the cohesin(s) and/or dockerin for their modular counterpart dictate the overall architecture of the cellulosome. Several different types of scaffoldins have been described: the primary scaffoldins incorporate the various dockerin-bearing subunits directly into the cellulosome complex, adaptor scaffoldins increase the repertoire or number of components into the complex, and the anchoring scaffoldins attach the complex to the bacterial cell surface.

* '''Cohesin modules''' are the major building blocks of scaffoldins, which are responsible for organizing the cellulolytic subunits into the multi-enzyme complex.

* '''Dockerin modules''' anchors the catalytic enzymes to the scaffoldin. It displays internal two-fold symmetry, consisting of a duplicated F-hand motif (a calcium-binding loop preceding an a helix). The dockerin could also be found in the C terminal of scaffoldins.

=== Cellulosome systems ===
Bacterial cellulosomal systems can be categorized into two major types: simple cellulosome systems contain a single scaffoldin and complex cellulosome systems exhibit multiple types of interacting scaffoldins. The arrangement of the modules on the scaffoldin subunit and the specificity of the cohesin(s) and/or dockerin for their modular counterpart dictate the overall architecture of the cellulosome. Several different types of scaffoldins have been described: the primary scaffoldins incorporate the various dockerin-bearing subunits directly into the cellulosome complex, adaptor scaffoldins increase the repertoire or number of components into the complex, and the anchoring scaffoldins attach the complex to the bacterial cell surface.

Cellulosomes exist as extracellular complexes that are either attached to the cell wall of bacteria or free in solution, where the insoluble substrate can be broken down into soluble products and taken up by the cell. The large size and heterogeneity of cellulosomes from the best-characterized organisms (i.e., ''C. thermocellum'', ''C. cellulolyticum'', and ''C. cellulovorans'') have greatly complicated efforts to probe cellulosome structure and function. Other cellulosome systems (such as those from ''Acetivibrio cellulolyticus'' and ''Ruminococcus flavefaciens'') appear to be even more intricate.

The genes encoding for many important cellulosome subunits are organized in “enzyme-linked gene clusters” on the chromosome.

'''Simple Cellulosome Systems'''

In the simple cellulosome systems, the scaffoldins contain a single CBM, one or more X2 modules and numerous (5 to 9) cohesins. These scaffoldins are primary scaffoldins, which incorporate the dockerin-bearing enzymes into the complex. In several cases, the simple cellulosomes have been shown to be associated with the cell surface, but the molecular mechanism responsible for this is still unclear. The X2 module may play a role in attachment to the cell wall (Fig).

'''Complex Cellulosome Systems'''

To date, complex cellulosome systems have been described in four different bacterial species (which…). In these systems, more than one scaffoldin interlocks with each other in various ways to produce a complex cellulosome architecture. At least one type of scaffoldin serves as a primary scaffoldin that incorporates the enzymes directly into the cellulosome complex. In each species, another type of scaffoldin attaches the cellulosome complex to the cell surface via a specialized module or sequence, designed for this purpose.
[[File:Clostridium_cellulosome.jpg|500px|alt text]]

== Cohesin-dockerin interactions ==
'''Cohesin-dockerin interactions''' can be viewed as a kind of plug-and-socket in which the dockerin plugs into the cohesin socket1. In general, the interaction is inter-species and intra-species (type) specific, however some cross-reactivity has been found in a few cases. In terms of strength, the cohesin-dockerin interaction is one of the most potent protein-protein interactions known in nature, in most cases approaching the strength of high-affinity antigen-antibody interactions (Ka ~ 1011 M-1).

So far, cohesins have been phylogenetically distributed into three groups according to sequence homology; the type-I cohesin, the type-II cohesin and the recently discovered type-III cohesin. The dockerins that interact with each cohesin type are, by definition, of the same type.

== Structural characterization of cellulosome components ==
One of the greatest efforts in the cellulosome research field is to understand the structure-function relationship in cellulosome assembly. Thus far, the crystallographic structure of only selected cohesins has been determined, including three different type-I cohesins, all of which share the typical jelly-roll topology that forms a flattened 9-stranded b-sandwich. The structures of four different type-II cohesins have also been determined. The type-II and type-III cohesins has the same jelly-roll topology as the type-I cohesins with several additional structural elements: an a-helix at the crown of the molecule (located in the loop connecting strands 6-7, and 8-9 for type-II and type-III, respectively), and two “b-flaps” that provisionally disrupt the normal course of b-strands 4 and 8 (Fig).

== History of discovery ==
In the early 1980s, Profs. Raffi Lamed and Ed Bayer met at Tel Aviv University and commenced their work that led to the discovery of the cellulosome concept. Raffi approached Ed at the time with a description of how ''Clostridium thermocellum'', an anaerobic thermophilic cellulolytic bacterium, bound very strongly to the cellulose substrate ''before'' it commences its degradation. They decided to study this phenomenon together.

At the time, they weren’t looking for enzymes or cellulosomes at all. They simply sought a ‘cellulose-binding factor’ or ‘CBF’ on the cell surface of the anaerobic thermophilic bacterium, ''Clostridium thermocellum,'' which they inferred would account for the observation that the bacterium attaches strongly to the insoluble cellulose substrate prior to its degradation. They employed a then unconventional experimental approach, in which they isolated an adherence-defective mutant of the bacterium and prepared a specific polyclonal antibody for detection of the functional component. Surprisingly, they isolated a very large multi-subunit supramolecular complex, instead of a small protein. Rather than discarding the uninvited material, they were alert enough to follow up this intriguing finding experimentally. A combination of biochemical, biophysical, immunochemical and ultrastructural techniques, followed by molecular biological verification, led to the definition and proof of the cellulosome concept. The birth of the discrete, multi-enzyme cellulosome complex was thus documented. Today, cellulosomes have been confirmed in several but not all cellulolytic bacteria. The cellulosome-producing strains exhibit surprising diversity in the composition and architecture of the component parts.

== References ==
<biblio>
#cellulosome1 pmid=15487947
#cellulosome2 pmid=20373916
#cellulosome3 pmid=19107866
#cellulosome4 pmid=17367380
#cellulosome5 pmid=15197390
</biblio>

[[Category:Definitions and explanations]]