InterPro: IPR018954 Beta-galactosidase, domain 2

This is the second domain of the five-domain beta-galactosidase enzyme that altogether catalyses the hydrolysis of beta(1-3) and beta(1-4) galactosyl bonds in oligosaccharides as well as the inverse reaction of enzymatic condensation and trans-glycosylation. This domain is made up of 16 antiparallel beta-strands and an alpha-helix at its C terminus. The fold of this domain appears to be unique. In addition, the last seven strands of the domain form a subdomain with an immunoglobulin-like (I-type Ig) fold in which the first strand is divided between the two beta-sheets. In penicillin spp this strand is interrupted by a 12-residue insertion which forms an additional edge-strand to the second beta-sheet of the sub-domain. The remainder of the second domain forms a series of beta-hairpins at its N terminus, four strands of which are contiguous with part of the Ig-like sub-domain, forming in total a seven-stranded antiparallel beta-sheet. This domain is associated with IPR001944, which is N-terminal to it, but itself has no metazoan members.