This is the C-terminal domain of Glycoside hydrolase 20 C (GH20C) present in S. pneumoniae. GH20C possesses the ability to hydrolyze the beta-linkages joining either N-acetylglucosamine or N-acetylgalactosamine to a wide variety of aglycon residues. The C-terminal domain is commonly known as Domain III is important in dimerization as it forms the primary interface of the dimer. However, there is presently no evidence supporting dimerization as being necessary for catalysis. Domain III is unusual among structurally characterized GH20 enzymes but in GH20 enzymes possessing domain III, dimerization seems to be a conserved feature [1].

1: A Second beta-Hexosaminidase Encoded in the Streptococcus pneumoniae Genome Provides an Expanded Biochemical Ability to Degrade Host Glycans. Robb M, Robb CS, Higgins MA, Hobbs JK, Paton JC, Boraston AB; J Biol Chem. 2015;290:30888-30900. PMID:26491009