The carbohydrate binding type-21 or CBM21 domain is a 90-130 amino acid
carbohydrate binding domain. The domain is named after proteins classified in
carbohydrate-binding module (CBM) family 21 and is sometimes called
starch-binding domain (SBD) [E1,1]. The CBM21 domain occurs in several
eukaryotic proteins implicated in glycogen metabolism. A glucoamylase active
site region (see <PDOC00646>) [E2] or α amylase catalytic domain [E3] can
occur C-terminal to the CBM21 domain. The CBM21 domain of Rhizopus oryzae
glucoamylase can bind to raw starch. Most conserved residues are located in a
region with a length of 35 in the N-terminal part  and in a 15-25 residue
motif II at the C-terminus of the domain [2,3,4].
Some proteins known to contain a CBM21 domain:
Mammalian protein phosphatase 1 (PP1) regulatory subunit 3A, which seems to
target PP1 to glycogen.
Mammalian protein phosphatase 1 binding protein PTG, which binds the 3 key
enzymes for the regulation of glycogen metabolism: phosphorylase kinase,
phosphorylase A and glycogen synthase.
Yeast protein phosphatase 1 regulatory subunits GAC1 and PIG1, which are
regulators of glycogen synthase.
Yeast GLC7-interacting protein 2 (GIP2), which interacts with the catalytic
subunit (GLC7) of PP1.
Yeast protein 2 interacting with GSY2 (PIG2), which interacts with glycogen
synthase 2 (GSY2), a nutritionally regulated form.
Rhizopus oryzae glucoamylase, which binds and hydrolyzes granular starch.
R. oryzae is a fungus from e.g. decaying vegetables and it causes
The profile we developed covers the entire CBM21 domain.
November 2005 / First entry.
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