3.A.1.2.1
Ribose porter.  RbsA has two ATPase domains fused together; RbsB is the substrate receptor; RbsC has 10 TMSs with N- and C-termini in the cytoplasm and forms a dimer (Stewart and Hermodson, 2003).  ABC importers can be divided into two classes. Type I importers follow an alternating access mechanism driven by the presence of the substrate. Type II importers accept substrates in a nucleotide-free state, with hydrolysis driving an inward-facing conformation.  RbsABC₂ seems to share functional traits with both type I and type II importers, as well as possessing unique features, and employs a distinct mechanism relative to other ABC transporters (Clifton et al. 2014).