In a process called quorum sensing, bacteria momentarily set aside their solitary lifestyle and commence working with like-minded neighbors, such as during the production of bioluminescence by the marine bacterium Vibrio harveyi. Genetics infused with biochemistry resulted in the identification and characterization of the autoinducer signal AI-2 and its receptor LuxP. The biosynthesis of AI-2 is controlled by the enzyme LuxS, which catalyzes the last step of the synthesis of the starting material (4S)-4,5-dihydroxy-2,3-pentanedione (DPD) from the common metabolite S-adenosylmethionine. In V. harveyi, DPD cyclizes to give (2S,4S)-2-methyl-2,3,3,4-tetra- hydroxytetrahydrofuran (S-THMF), which reacts with boron to form S-THMF-borate, the actual ligand of LuxP.
Miller et al. have solved the structure of the periplasmic protein LsrB, the Salmonella typhimurium counterpart to LuxP, and find that its ligand is a slightly different DPD derivative, (2R,4S)-2-methyl-2,3,3,4-tetrahydroxytetrahydrofuran (R-THMF) and that no boron is present. As in the case of LuxP, crystallization of the LsrB-ligand complex facilitated chemical characterization of the ligand, and the net negative charge within the LsrB binding cleft (unlike the positive charge in LuxP) suggests that it would not recognize S-THMF-borate. This diversity of autoinducer metabolites raises the possibility that bacteria might have enough bandwidth to receive multiplexed signals. -- GJC
Mol. Cell 15, 677 (2004).
