Modulation of functionally significant conformational equilibria in adenylate kinase by high concentrations of trimethylamine oxide attributed to volume exclusion |
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| Authors: | Nagarajan Sureshbabu Amir Dan Grupi Asaf Goldenberg David P Minton Allen P Haas Elisha |
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| Institution: | †The Goodman Faculty of Life Sciences, Bar Ilan University, Ramat Gan, Israel;‡Department of Biology, University of Utah, Salt Lake City, Utah;§Section on Physical Biochemistry, Laboratory of Biochemistry and Genetics, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland |
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| Abstract: | The effect of an inert small molecule osmolyte, trimethyl amine N-oxide (TMAO), upon the conformational equilibria of Escherichia coli adenylate kinase was studied using time-resolved FRET. The relative populations of open and closed clefts between the LID and the CORE domains were measured as functions of the concentrations of the substrate ATP over the concentration range 0–18 mM and TMAO over the concentration range 0–4 M. A model was constructed according to which the enzyme exists in equilibrium among four conformational states, corresponding to combinations of open and closed conformations of the LID-CORE and AMP-CORE clefts. ATP is assumed to bind only to those conformations with the closed LID-CORE cleft, and TMAO is assumed to be differentially excluded as a hard spherical particle from each of the four conformations in accordance with calculations based upon x-ray crystallographic structures. This model was found to describe quantitatively the dependence of the fraction of the closed LID-CORE cleft upon the concentrations of both ATP and TMAO over the entire range of concentrations with just five undetermined parameters. |
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