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| {{STRUCTURE_1hw5| PDB=1hw5 | SCENE= }} | | {{STRUCTURE_1hw5| PDB=1hw5 | SCENE= }} |
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| '''THE CAP/CRP VARIANT T127L/S128A'''
| | ===THE CAP/CRP VARIANT T127L/S128A=== |
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| ==Overview==
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| 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 A. 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 C-terminal domain. In addition, water-mediated interactions replace the hydrogen bonding interactions between the N(6) of anti-cAMP bound in the N-terminal domains of each subunit and the OH groups of the Thr(127) and Ser(128) residues in the C alpha-helix of wild type CRP. This replacement induces flexibility in the C alpha-helix at Ala(128), which swings the C-terminal domain of the open subunit more toward 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 CRP by Passner and Steitz (Passner, J. M., and Steitz, T. A. (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 flexibility at Ala(128) and/or by the bound syn-cAMP in the hinge region of CRP*. | | The line below this paragraph, {{ABSTRACT_PUBMED_11124966}}, adds the Publication Abstract to the page |
| | (as it appears on PubMed at http://www.pubmed.gov), where 11124966 is the PubMed ID number. |
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| | {{ABSTRACT_PUBMED_11124966}} |
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| ==About this Structure== | | ==About this Structure== |
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| [[Category: Camp receptor protein]] | | [[Category: Camp receptor protein]] |
| [[Category: Cyclic amp mutant]] | | [[Category: Cyclic amp mutant]] |
| ''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Fri May 2 19:17:28 2008'' | | |
| | ''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Mon Jul 28 03:45:01 2008'' |