Cyclic di-GMP allosterically inhibits the CRP-like protein (Clp) of Xanthomonas axonopodis pv. citri

Abstract

The protein Clp from Xanthomonas axonopodis pv. citri regulates pathogenesis and is a member of the CRP (cyclic AMP receptor protein) superfamily. We show that unlike the DNA-binding activity of other members of this family, the DNA-binding activity of Clp is allosterically inhibited by its effector and that cyclic di-GMP serves as that effector at physiological concentrations.

FIG. 1.

Extent of DNA binding by CRP in the presence of 1 mM cAMP compared to that of C-terminally His-tagged X. axonopodis Clp in the absence of any effector, as determined by fluorescence anisotropy using 10 nM CCpmelR DNA probe. Data points for Clp are compiled from two independent experiments.

FIG. 2.

c-di-GMP inhibition of DNA binding by C-terminally His-tagged X. axonopodis Clp as measured by fluorescence anisotropy, using 200 nM protein. A single point shows the restoration of DNA binding upon addition of 5 mM cAMP to the 10 μM c-di-GMP-inhibited Clp sample.