Part of an ABC transporter complex involved in ultra-high affinity tungstate uptake. Specifically binds tungstate. The complex is composed of two ATP-binding proteins (TupC), two transmembrane proteins (TupB) and a solute-binding protein (TupA). Mutants contain the same concentration of molybdenum but they show a 75% reduction in tungsten concentration and a 50% reduction in formate dehydrogenase (FDH) activity. Binds tungstate 50'000-fold more tightly than molybdate.