Quorum Sensing

molecules able to interfere with AI-2 QS could lead to the develop-

ment of next generation broad-spectrum antimicrobial agents [21].

As the predominant precursor for all AI-2 signals, 4,5-dihy-

droxy-2,3-pentandione (DPD) can undergo cyclization and addi-

tional reactions spontaneously to generate distinct AI-2 signal

molecules. For example,S-THMF-borate, a boron-containing AI-

2 molecule, is used as autoinducer inV. harveyi.InV. harveyi, two

proteins, LuxP and LuxQ are involved in the response to AI-2.

LuxP is a periplasmic-binding protein and LuxQ is a two-

component hybrid sensor kinase [22]. LuxP binds to LuxQ as a

complex named LuxPQ [23]. In 2002, the crystal structure of the

receptor LuxP fromV. harveyiwith AI-2 was determined [22].

Moreover, the crystal structure of the AI-2-LuxPQ complex was

resolved by the Hughson group in 2006 [24].

As shown in Fig.1, when cell density is low, autophosphoryla-

tion of LuxQ leads to convey phosphate through LuxU to LuxO.

Phosphorylated LuxO cooperates withσ^54 and promotes the pro-

duction of small regulatory RNAs. As a consequence, mRNA of the

transcriptional regulators LuxR is destabilized, and LuxR-

dependent genes are not transcribed. Conversely, at high cell den-

sity AI-2 binds to LuxP and induces the LuxPQ complex to initiate

Fig. 1Mechanism of AI-2 mediated quorum sensing inV. harvyi

354 Tianyu Jiang et al.