The TOBE domain [1] (Transport-associated OB) always occurs as a dimer as the C-terminal strand of each domain is supplied by the partner. Probably involved in the recognition of small ligands such as molybdenum (eg Swiss:P46930) and sulfate (Swiss:P16676). Found in ABC transporters immediately after the ATPase domain.

1: Protein fold recognition using sequence profiles and its application in structural genomics. Koonin EV, Wolf YI, Aravind L; Adv Protein Chem 2000;54:245-275. PMID:10829230