Fig. 5

Binding of LsrB to endogenous AI-2. Purified LsrB (BL21) and LsrB (BL21∆luxS) proteins (5 mg/ml) were incubated for 10 min at 37, 50 and 60 °C to release endogenous AI-2, respectively. After incubation, the LsrB proteins were removed by ultrafiltration (10,000-Da cut-off; EMD Millipore), and the filtered reaction products were tested for AI-2 activity using a V. harveyi BB170 bioassay. The extent of LsrB binding to endogenous AI-2 was evaluated using an AI-2 assay, which showed that recombinant LsrB (BL21) bound to endogenous AI-2 (produced by wild-type strain BL21) and was released from LsrB (BL21) at 50 or 60 °C, respectively (a). However, since the luxS mutant BL21∆luxS did not produce endogenous AI-2, no AI-2 could be released from the recombinant LsrB (BL21∆luxS) (b). Moreover, the recombinant LuxS protein, which was expressed in strain BL21 (pColdTF-lsrB) as a negative control, also showed no AI-2 binding activity (c). AI-2 (10 μM) was used as a positive control