{PDOC51166}
{PS51166; CBM20}
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* CBM20 (carbohydrate binding type-20) domain profile *
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Carbohydrate-binding  modules  (CBM)  have  been  classified into more than 40
families according to sequence homology [E1]. Several amylolytic enzymes share
a  conserved  region  of  90-130  amino acid residues, the CBM20 domain. It is
mainly  found  C-terminal  to  the catalytic domain and has been shown to bind
granular starch [1,2].

The  crystal  structure  of  CBM20  has  been  solved (see <PDB:1CGT>) [3]. It
consists  of  seven  beta-stands  forming an open-sided distorted beta-barrel.
Several  aromatics,  especially  the  well-conserved  Trp  and  Tyr  residues,
participates  in  granular  starch  binding.  Starch consists of glucose units
mainly  in  the  form  of  amylose  and  amylopectin,  which  are  arranged in
semicrystalline  arrays  of  double-helical  strands  to  form large irregular
granules.  The  two  starch  strands  are  bound  to  the  CBM20  domain  in a
perpendicular orientation. This may be functionally important, as it may force
starch strands apart thus increasing the hydrolyzable surface [4].

Some proteins known to contain a CBM20 domain are listed below:

 - Mammalian genethonin 1 protein.
 - Mammalian  laforin protein, a dual specificity protein phosphatase that may
   be involved in the control of glycogen metabolism.
 - Human hypothetical protein KIAA1434.
 - Fungi glucoamylase (EC 3.2.1.3).
 - Bacterial cyclomaltodextrin glucanotransferase (EC 2.4.1.19).
 - Bacterial alpha-amylase (EC 3.2.1.1).
 - Pseudomonas  glucan 1,4-alpha-maltotetraohydrolase precursor (EC 3.2.1.60).
 - Thermoanaerobacterium amylopullulanase  (Alpha-amylase/pullulanase).
 - Bacillus maltogenic alpha-amylase (EC 3.2.1.133).

The profile we developed covers the whole CBM20 domain.

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

-Note: The CBM20 domain is also known as the starch-binding domain.

-Last update: November 2005 / First entry.

[ 1] Goto M., Semimaru T., Furukawa K., Hayashida S.
     "Analysis of the raw starch-binding domain by mutation of a
     glucoamylase from Aspergillus awamori var. kawachi expressed in
     Saccharomyces cerevisiae."
     Appl. Environ. Microbiol. 60:3926-3930(1994).
     PubMed=7993082
[ 2] Chen L., Coutinho P.M., Nikolov Z., Ford C.
     "Deletion analysis of the starch-binding domain of Aspergillus
     glucoamylase."
     Protein Eng. 8:1049-1055(1995).
     PubMed=8771186
[ 3] Klein C., Schulz G.E.
     "Structure of cyclodextrin glycosyltransferase refined at 2.0 A
     resolution."
     J. Mol. Biol. 217:737-750(1991).
     PubMed=1826034
[ 4] Sorimachi K., Le Gal-Coeffet M.F., Williamson G., Archer D.B.,
     Williamson M.P.
     "Solution structure of the granular starch binding domain of
     Aspergillus niger glucoamylase bound to beta-cyclodextrin."
     Structure 5:647-661(1997).
     PubMed=9195884
[E1] http://www.cazy.org/CBM20.html

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