Part of the ABC transporter complex ThiBPQ involved in thiamine import (PubMed:12175925). Binds thiamine, thiamine phosphate and thiamine diphosphate with high affinity (PubMed:12182833, PubMed:18177053). Transport is inhibited by the sulfhydryl-specific modifier N-ethylmaleimide. Monomer in solution (PubMed:12182833). The complex is composed of two ATP-binding proteins (ThiQ), two transmembrane proteins (ThiP) and a solute-binding protein (ThiB) (By similarity). Belongs to the bacterial solute-binding protein 1 family.