{PDOC00485}
{PS00561; CBM2_A}
{PS51173; CBM2}
{BEGIN}
*******************************************************************
* CBM2 (carbohydrate-binding type-2) domain signature and profile *
*******************************************************************

The  microbial  degradation  of cellulose and xylans requires several types of
enzyme  such  as endoglucanases (EC 3.2.1.4), cellobiohydrolases (EC 3.2.1.91)
(exoglucanases),  or  xylanases (EC 3.2.1.8) [1]. Structurally, cellulases and
xylanases  generally  consist  of a catalytic domain and a conserved region of
~100  amino acid residues, the carbohydrate-binding module 2 (CBM2) [2,E1]. It
is  found  either  at  the  N-terminal or at the C-terminal extremity of these
enzymes.

CBM2  can be classified in 2 subfamilies according to substrate specificities:
CBM2a which binds cellulose and CBM2b which interacts specifically with xylan.
CBM2a  and  CBM2b also display significant differences at the residue level as
shown in the following schematic representation:

           +-------------------------------------------------+
           |                                                 |
 CBM2a    xCxxxxWxxGxxNxxxxxxxxxxxWxxxxxxxxWNxxxxxGxxxxxxxxxxCx
                                           ********

           +-------------------------------------------------+
           |                                                 |
 CBM2b    xCxxxxWxxRxxNxxxxxxxxxxxWxxxxxxx--------GxxxxxxxxxxCx

'C': conserved cysteine involved in a disulfide bond.
'*': position of the pattern.
'W': surface-exposed tryptophan

Like  other  CBM  domains CBM2 is a beta-sheet domain containing a planar face
which  interacts  with its ligand via a hydrophobic strip of aromatic residues
(see  <PDB:1EXG>) [3]. In family 2a this hydrophobic surface consists of three
tryptophan  residues, which are all required for binding soluble and insoluble
forms  of  cellulose  [4]. In family 2b only 2 surface-exposed tryptophans are
conserved  and the first one is oriented differently. It is therefore not well
oriented to interact with cellulose but is ideal for binding xylan [5].

Enzymes known to contain such a domain are:

 - Endoglucanase (gene end1) from Butyrivibrio fibrisolvens.
 - Endoglucanases A (gene cenA) and B (cenB) from Cellulomonas fimi.
 - Exoglucanases A (gene cbhA) and B (cbhB) from Cellulomonas fimi.
 - Endoglucanase E-2 (gene celB) from Thermomonospora fusca.
 - Endoglucanase A (gene celA) from Microbispora bispora.
 - Endoglucanases A  (gene celA),  B (celB)  and  C  (celC)  from  Pseudomonas
   fluorescens.
 - Endoglucanase A (gene celA) from Streptomyces lividans.
 - Exocellobiohydrolase (gene cex) from Cellulomonas fimi.
 - Xylanases A (gene xynA) and B (xynB) from Pseudomonas fluorescens.
 - Arabinofuranosidase C   (EC 3.2.1.55)    (xylanase C)    (gene xynC)   from
   Pseudomonas fluorescens.
 - Chitinase 63 (EC 3.2.1.14) from Streptomyces plicatus.
 - Chitinase C from Streptomyces lividans.

To  recognize  the  CBM2a  domain we developed a pattern which is located in a
conserved  region  specific to CBM2a. We also developed a profile which covers
the whole CBM2 domain and recognizes both CBM2 subfamilies.

-Consensus pattern: W-N-[STAGR]-[STDN]-[LIVM]-x(2)-[GST]-x-[GST]-x(2)-
                    [LIVMFT]-[GA]
-Sequences known to belong to this class detected by the profile: ALL.
-Other sequence(s) detected in Swiss-Prot: NONE.

-Sequences known to belong to this class detected by the profile: ALL.
-Other sequence(s) detected in Swiss-Prot: NONE.

-Last update: December 2005 / Text revised; profile added.

[ 1] Gilkes N.R., Henrissat B., Kilburn D.G., Miller R.C. Jr., Warren R.A.J.
     "Domains in microbial beta-1, 4-glycanases: sequence conservation,
     function, and enzyme families."
     Microbiol. Rev. 55:303-315(1991).
     PubMed=1886523
[ 2] Meinke A., Gilkes N.R., Kilburn D.G., Miller R.C. Jr., Warren R.A.J.
     "Bacterial cellulose-binding domain-like sequences in eucaryotic
     polypeptides."
     Protein Seq. Data Anal. 4:349-353(1991).
     PubMed=1812490
[ 3] Xu G.Y., Ong E., Gilkes N.R., Kilburn D.G., Muhandiram D.R.,
     Harris-Brandts M., Carver J.P., Kay L.E., Harvey T.S.
     "Solution structure of a cellulose-binding domain from Cellulomonas
     fimi by nuclear magnetic resonance spectroscopy."
     Biochemistry 34:6993-7009(1995).
     PubMed=7766609
[ 4] Nagy T., Simpson P., Williamson M.P., Hazlewood G.P., Gilbert H.J.,
     Orosz L.
     "All three surface tryptophans in Type IIa cellulose binding domains
     play a pivotal role in binding both soluble and insoluble ligands."
     FEBS. Lett. 429:312-316(1998).
     PubMed=9662439
[ 5] Simpson P.J., Bolam D.N., Cooper A., Ciruela A., Hazlewood G.P.,
     Gilbert H.J., Williamson M.P.
     "A family IIb xylan-binding domain has a similar secondary structure
     to a homologous family IIa cellulose-binding domain but different
     ligand specificity."
     Structure. Fold. Des. 7:853-864(1999).
     PubMed=10425686
[ 6] Simpson P.J., Xie H., Bolam D.N., Gilbert H.J., Williamson M.P.
     "The structural basis for the ligand specificity of family 2
     carbohydrate-binding modules."
     J. Biol. Chem. 275:41137-41142(2000).
     PubMed=10973978; DOI=10.1074/jbc.M006948200
[E1] http://www.cazy.org/CBM2.html

--------------------------------------------------------------------------------
PROSITE is copyrighted by the SIB Swiss Institute of Bioinformatics and
distributed under the Creative Commons Attribution-NonCommercial-NoDerivatives
(CC BY-NC-ND 4.0) License, see https://prosite.expasy.org/prosite_license.html
--------------------------------------------------------------------------------

{END}