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Sturcture of Coumarin 153: A very well studied probe for solvation |
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Studies of the solvation dynamics in proteins offer the best means of investigating the dielectric response and making a comparison with theory. A range of theoretical and experimental work has been performed to study dielectric responses in proteins; but the results have been very disparate. In order to study the dielectric response in proteins, it is of extreme importance to have a model system. Towards this goal, we have proposed that the complex of apomyoglobin/C153 as a model system to study the dielectric response in protein environment and presented result from solvation dynamics experiments of the complexes of coumarin 153 (C153) with the monomeric hemeproteins, apomyoglobin and apoleghemoglobin, in water. |
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Holomyoglobin |
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Apomyoglobin |
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Coumarin 153/Apomyoglobin |
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Heme Proteins |
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Four main considerations for the choice of C153/ApoMb system: 1. C153 is a well characterized and widely used chromophore for solvation dynamics studies, 2. Binding studies and molecular dynamics simulations indicate that coumarin indeed is in the hemepocket. We have experimentally obtained a binding constant of ~ 6 mM for coumarin 153 and apomyoglobin from Job’s plot (Figure left), 3. Although myoglobin and leghemoglobin share a common globin fold, they have differences in their hemepockets, the region to be probed by the coumarin, 4. A broad range of mutant proteins can be produced in which one or several amino acids are strategically replaced, so as to test how specific substitutions can affect solvation dynamics |
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Main Outcomes : 1. Almost 60 % of the solvation is complete in both apoMb and apoLba within the time resolution of our instrument (300 fs). 2. The initial faster solvation is followed by a slower response, which is slower in apoLba than in apoMb by about a factor of 4. 3. There is excellent agreement between the C(t) from fluorescence upconversion experiments and those obtained from molecular dynamics simulations. |
