Small angle scattering measurements were performed on solutions of cAMP receptor protein (CRP) and on solutions of the T127->A double mutant of CRP (DM) in D2O K3PO4 buffer containing 0.6 M KCl, in the absence and presence of 3',5' cyclic adenosine monophosphate (cAMP). Energy-minimized structures of the CRP were calculated by minimization of the x-ray crystallographic structure of CRP in either the exclusively closed form where the alpha-helices of the carboxyl terminal domain are folded close to the amino terminal domain and in the exclusively open form where the alpha-helices of the carboxyl terminal domain are folded away from the amino terminal domain. Neutron scattering models show that the CRP SANS data follow closely the data curve predicted for unligated CRP in the open form while the cAMP-ligated data are more in agreement with the data predicted for the minimized cAMP-ligated CRP structure in the closed form. The SANS data from the DM and cAMP-ligated DM are coincidental which implies that there is very little structural difference between the two species of DM. This is in agreement with in vivo results which show that CRP undergoes a conformational change upon ligation with cAMP to activate transcription in the cell while DM activates transcription in the absence of cAMP, implying that it is already in the correct conformation for the activation of transcription.
Citation: Journal of Biological Chemistry
Pub Type: Journals
cAMP receptor protein, energy minimization, small angle neutron scattering, solvent, structure