Part of the tripartite efflux system MacAB-TolC. MacB is a non-canonical ABC transporter that contains transmembrane domains (TMD), which form a pore in the inner membrane, and an ATP-binding domain (NBD), which is responsible for energy generation. When overexpressed, the system confers resistance against macrolides composed of 14- and 15-membered lactones but no or weak resistance against 16-membered ones. In addition, the system could also transport R-LPS or a similar glycolipid. ATPase activity is stimulated by interaction with MacA and inhibited by vanadate. kcat is 0.78 sec(-1) for ATP in the presence of MacA. kcat is 0.10 sec(-1) for ATP in the absence of MacA. Homodimer. Part of the tripartite efflux system MacAB-TolC, which is composed of an inner membrane transporter, MacB, a periplasmic membrane fusion protein, MacA, and an outer membrane component, TolC. The complex forms a large protein conduit and can translocate molecules across both the inner and outer membranes. Interacts with MacA. Belongs to the ABC transporter superfamily. Macrolide exporter (TC 3.A.1.122) family.