Skip to main content
U.S. flag

An official website of the United States government

Official websites use .gov
A .gov website belongs to an official government organization in the United States.

Secure .gov websites use HTTPS
A lock ( ) or https:// means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites.

The Structure of the T127L/S128A Mutant of cAMP Receptor Protein Facilitates Promoter Site Binding



S. Chu, M. Tordova, G L. Gilliland, I Gorshkova, Y. Shi, S. Wang, Frederick P. Schwarz


The x-ray crystal structure of the cAMP-ligated T127L/S128A double mutant of cAMP receptor protein (CRP) was determined to a resolution of 2.2 . Although this structure is close to that of the x-ray crystal structure of cAMP-ligated CRP with one subunit in the open form and one subunit in the closed form, a bound syn-cAMP is clearly observed in the closed subunit in a third binding site in the closed subunit in a third binding site in the C-terminal domain. In addition, water-mediated interactions replace the hydrogen bonding interactions between the N6 of anti-cAMP bound in the N-terminal domains of each subunit and the OH groups of the Thr127 and Ser128 residues in the C α-helix of wild type CRP. This replacement induces flexibility in the C α-helix at Ala128, which swings the C-terminal domain of the open subunit more towards the N-terminal domain in the T127L/S128A double mutant of CRP(CRP*) than is observed in the open subunit of cAMP-ligated CRP. Isothermal titration calorimetry measurements on the binding of cAMP to CRP* show that the binding mechanism changes from an exothermic independent two-site binding mechanism at pH 7.0 to an endothermic interacting two-site mechanism at pH 5.2, similar to that observed for CRP at both pH levels. Differential scanning calorimetry measurements exhibit a broadening of the thermal denaturation transition of CRP* relative to that of CRP at pH = 7.0, but similar to the multipeak transitions observed for cAMP-ligated CRP. These properties and the bound syn-cAMP ligand, which has only been previously observed in the DNA bound x-ray crystal structure of cAMP-ligated by Passner and Steitz, (1997) Proc. Natl. Acad. Sci., U.S.A.94, 2843-2847, imply that the cAMP-ligated CRP* structure is closer to the conformation of the allosterically-activated structure than cAMP-ligated CRP. This may be induced by the unique pivotal point at Ala128 and/or by the bound syn-cAMP in the hinge region of CRP*.
Journal of Biological Chemistry


CAMP receptor protein, catabolate activator protein, differential scanning calorimetry, isothermal titration calorimetry, x-ray crystallography


Chu, S. , Tordova, M. , Gilliland, G. , Gorshkova, I. , Shi, Y. , Wang, S. and Schwarz, F. (2001), The Structure of the T127L/S128A Mutant of cAMP Receptor Protein Facilitates Promoter Site Binding, Journal of Biological Chemistry (Accessed June 23, 2024)


If you have any questions about this publication or are having problems accessing it, please contact

Created April 5, 2001, Updated October 12, 2021