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Thermodynamic analysis of hydration in human serum heme-albumin |
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| Authors: | Simona Baroni Gabriella Fanali Paolo Ascenzi Mauro Fasano |
| Institution: | a Invento S.r.l., “Companies Incubator” of the University of Torino, Via Nizza 52, I-10126, Torino, Italy b Department of Structural and Functional Biology, and Center of Neurosciences, University of Insubria, Via Alberto da Giussano 12, I-21052 Busto Arsizio (VA), Italy c Department of Chemistry I.F.M. and Center of Molecular Imaging (CIM), University of Torino, Via Nizza 52, I-10126 Torino, Italy d Department of Biology and Interdepartmental Laboratory for Electron Microscopy, Viale Guglielmo Marconi 446, University ‘Roma Tre’, I-00146 Roma, Italy |
| Abstract: | Ferric human serum heme-albumin (heme-HSA) shows a peculiar nuclear magnetic relaxation dispersion (NMRD) behavior that allows to investigate structural and functional properties. Here, we report a thermodynamic analysis of NMRD profiles of heme-HSA between 20 and 60 °C to characterize its hydration. NMRD profiles, all showing two Lorentzian dispersions at 0.3 and 60 MHz, were analyzed in terms of modulation of the zero field splitting tensor for the S = 5/2 manifold. Values of correlation times for tensor fluctuation (τv) and chemical exchange of water molecules (τM) show the expected temperature dependence, with activation enthalpies of −1.94 and −2.46 ± 0.2 kJ mol−1, respectively. The cluster of water molecules located in the close proximity of the heme is progressively reduced in size by increasing the temperature, with ΔH = 68 ± 28 kJ mol−1 and ΔS = 200 ± 80 J mol−1 K−1. These results highlight the role of the water solvent in heme-HSA structure-function relationships. |
| Keywords: | HSA human serum albumin Ferric heme-HSA ferric human serum heme-albumin MR magnetic resonance NMRD nuclear magnetic relaxation dispersion ZFS zero field splitting PBS phosphate buffered saline |
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