Part of the ABC transporter complex LsrABCD involved in autoinducer 2 (AI-2) import. Binds AI-2 and delivers it to the LsrC and LsrD permeases (By similarity). The complex is composed of two ATP-binding proteins (LsrA), two transmembrane proteins (LsrC and LsrD) and a solute-binding protein (LsrB). Belongs to the bacterial solute-binding protein 2 family.