This invention relates to crystals comprising apo-LsrB and holo-LsrB. The structure of holo-LsrB identifies a tetrahydroxytetrahydrofuran derived from 4,5-dihydroxy-2,3-pentanedione (DPD) as the active autoinducer-2 (AI-2) molecule in Salmonella typhimurium. The X-ray crystallographic data can be used in a drug discovery method. Additionally the invention provides AI-2 analogs based on this discovery as well as pharmaceutical compositions containing those analogs.