PROSITE documentation PDOC52006

Glycosyl hydrolases family 64 (GH64) domain profile

The glycoside hydrolases (GHs, EC 3.2.1.-) are a diverse set of enzymes with a vast range of substrate specificity. GHs hydrolyze the glycosidic bond between two or more carbohydrates or between a carbohydrate and non-carbohydrate moiety. These enzymes play diverse roles in nature; they breakdown cellulose into smaller carbohydrates (i.e. during biomass degradation by cellulases), they function during pathogenesis such as the activity of influenza virus neuraminidase, and they are engaged in normal cellular metabolic processes that involve the formation and breakage of glycosidic bonds along with glycosyl transferase. All reported GH family 64 (GH64) members are laminaripentaose-producing "inverting" β-1,3-glucanases [E1]. These enzymes cleave the β-1,3-bonds found in a variety of β-1,3-glucans such as laminarin or pachyman. "Inverting" enzymes utilize a single-displacement reaction where an activated water molecule performs a nucleophilic attack at the sugar C-1 while concomitant aglycone departure is achieved by protonation of the glycosidic oxygen [1,2,3,4].

The GH64 domain is composed of a barrel subdomain comprising mainly β-strands and a mixed (α/β) subdomain comprising helices and β-strands (see <PDB:3GD0>). It takes the form of a crescent, with a wide-open groove present for ligand binding. This wide groove is located between the β-barrel subdomain and the mixed α/β-subdomain and the ligand-binding cleft in it is lined by negatively charged residues. Two strictly conserved catalytic residues, a Glu and an Asp, lie one-third of the way down the groove and act as an acid catalyst and a base catalyst, respectively [2,4].

Some proteins known to contain a GH64 domain are listed below:

• Streptomyces matensis laminaripentaose hydrolase (SmLPHase), cleaves a long-chain polysaccharide, β-1,3-glucan, including laminarin, into a specific pentasaccharide oligomer "laminaripentaose" [1,2].
• Paenibacillus barengoltzii GH family 64 β-1,3-glucanase (PbBgl64A), a multi-domain protein that belongs to the GH64-TLP superfamily, which consists of an N-terminal CBM56 domain and a C-terminal family 64 GH domain [3].
• Clostridium beijerinckii glucanallin, composed of a βγ-crystallin domain (see <PDOC00197>), a GH64 domain, and a CBM56 domain [4].

The profile we developed covers the whole GH64 domain.