Structural domains comprising this superfamily share the structure of domain A 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. Domains A is mainly composed of beta-strands and is sequentially non-contiguous. The first three domains in Tp47 interact closely with each other through intimate domain-domain interfaces. Domain A contacts domain B through its N-terminal segment and it also interacts tightly with domain C PMID:12196546.