Dephosphorylation of the Escherichia coli transcriptional antiterminator BglG by the sugar sensor BglF is the reversal of its phosphorylation

The Escherichia coli BglF protein catalyzes transport and phosphorylation o f beta-glucosides. In addition, BglF is a membrane sensor which reversibly phosphorylates the transcriptional regulator BglG, depending on beta-glucos ide availability. Therefore, BglF has three enzymatic activities: beta-gluc oside phosphotransferase, BglG phosphorylase, and phospho-BglG (BglG-P) dep hosphorylase. Cys-24 of BglF is the active site which delivers the phosphor yl group either to the sugar or to BglG. To characterize the dephosphorylas e activity, we asked whether BglG-P can give the phosphoryl group back to C ys-24 of BglF. Here we provide evidence which is consistent with the interp retation that Cys-24-P is an intermediate in the BglG-P dephosphorylation r eaction. Hence, the dephosphorylation reaction catalyzed by BglF proceeds v ia reversal of the phosphorylation reaction.