The bacterial phosphoenolpyruvate: sugar phosphotransferase system (PTS) is a multi-protein system involved in the regulation of a variety of metabolic and transcriptional processes. The lactose/cellobiose-specific family are one of four structurally and functionally distinct group IIA PTS system enzymes. This family of proteins normally function as a homotrimer, stabilised by a centrally located metal ion [1]. Separation into subunits is thought to occur after phosphorylation.

1: The structure of enzyme IIAlactose from Lactococcus lactis reveals a new fold and points to possible interactions of a multicomponent system. Sliz P, Engelmann R, Hengstenberg W, Pai EF; Structure 1997;5:775-788. PMID:9261069