Structural domains comprising this superfamily share the structure of domain C of the unusual penicillin-binding protein (PBP), Tp47. Tp47 is unusual in that it displays beta-lactamase activity, so it does not fit the classical PBP archetype, and thus it appears to represent a new class of PBP. Domain C is the largest domain is the largest domain in this protein and it presents an immunoglobulin fold with two opposing beta-sheets that form the typical barrel-like structure. However, compared to the classical immunoglobulin fold domain C of cTp47 has an additional beta-strand inserted after strand 3 and in it the strands are connected by rather large loops. Helices are also inserted between strands 2 and 3 and between strands 4 and 5. Domain C interacts with domain B via a surface that has a slightly concave, goblet-like shape in addition to interacting tightly with domain A and weakly with domain D PMID:12196546.