Part of the OusB ABC transporter complex involved in glycine betaine and choline uptake. May also transport several other osmoprotectants such as ectoine, DMSA, DMSP, proline and carnitine. Probably responsible for energy coupling to the transport system. The complex is composed of two ATP-binding proteins (OusV), two transmembrane proteins (OusW) and a solute-binding protein (OusX). Induced by increased medium osmolality. Repressed by glycine betaine. Uptake of glycine betaine and choline is completely abolished in the ousA-ousB double mutant. Belongs to the ABC transporter superfamily.