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 (Probable). The complex is composed of two ATP-binding proteins (LsrA), two transmembrane proteins (LsrC and LsrD) and a solute-binding protein (LsrB). In the absence of AI-2, repressed by LsrR. Induced by AI-2, via release of the LsrR repressor. Belongs to the bacterial solute-binding protein 2 family.