Glycoside hydrolases (GHs, EC 3.2.1.-) form a widespread group of enzymes that hydrolyze the glycoside bond between monosaccharide units or between a carbohydrate and an aglycone moiety. GHs can act specifically as exo-cleaving enzymes to remove the sugar units from the ends of chains and release small sugar products, or endo-cleaving enzymes to act within the polysaccharide chain and produce oligosaccharides. The GH family 81 (GH81) includes proteins with endo-β-1,3-glucanase widely distributed in plants, fungi, bacteria, archaea and viruses. GH81 proteins show rather diverse physiological roles. These proteins share a common region of around 650 amino acids that is characteristic of the family [1,2,3,4].

The core catalytic domain of family 81 GHs consists of an N-terminal β-sandwich subdomain, a C-terminal (α/β)6 barrel subdomain and an additional α/β-subdomain between them (see <PDB:4K3A>). The β-sandwich subdomain compacts with (α/β)6 barrel subdomain and forms a long binding cleft. Along the catalytic cleft there are a number of aromatic residues that are conserved in GH family 81 glucanases and may be involved in stacking interactions with the rings of the glucosyl residues of the substrate. Three amino acid residues that are conserved in the family have been proposed as candidate catalytic residues: an aspartate (acid catalyst) and two glutamates (proton donor and basic catalyst respectively). These residues are located in the base of the catalytic cleft present near the center of the (α/β)6 barrel [2,3,4].

Some proteins known to contain a GH81 domain are listed below:

• Schizosaccharomyces pombe β-1,3-Endoglucanase (SpEng1), an extracellular protein that plays a critical role in cell cycle by helping in the dissolution of the septum.
• Schizosaccharomyces pombe β-1,3-endoglucanase (SpEng2), an intracellular cytoplasmic protein involved in actin assembly.
• Saccharomyces cerevisiae ScEng1, an extracellular protein that acts together with the Cts1 chitinase during cell separation to hydrolyze the cell wall components of the septum.
• Saccharomyces cerevisiae ScEng2, an intracellular cytoplasmic protein.
• Candida albicans β-1,3-endoglucanase (CAENG1), involved in cell wall separation.
• Pneumocystis sp. β-1,3-endoglucanase, regulates cell-wall β-glucan processing during its life cycle.
• Rhizomucor miehei RmLam81A.
• Plant β-glucan-elicitor-binding-proteins (GBPs) that are usually found in the plasma membrane and are pasrt of a defense mechanism against fungal infection.
• Paenibacillus sp. β-1,3-glucanas LamA.
• Clostridium thermocellum Eng1 (CtLam81A), a β-1,3-glucanase belonging to cellulosomal complex.

The profile we developed covers the whole GH81 domain.