title: The five-to-six-coordination transition of ferric human serum heme-albumin is allosterically-modulated by ibuprofen and warfarin: a combined XAS and MD study.
abstract: Human serum albumin (HSA) is involved physiologically in heme scavenging; in turn, heme-albumin (HSA-heme-Fe) displays globin-like properties. Here, the allosteric effect of ibuprofen and warfarin on the local atomic structure around the ferric heme-Fe (heme-Fe(III)) atom of HSA-heme-Fe (HSA-heme-Fe(III)) has been probed by Fe-K edge X-ray absorption spectroscopy (XAS). The quantitative analysis of the Fe-K edge extended X-ray absorption fine structure (EXAFS) signals and modeling of the near edge (XANES) spectral features demonstrated that warfarin and ibuprofen binding modify the local structure of the heme-Fe(III). Combined XAS data analysis and targeted molecular dynamics (MD) simulations provided atomic resolution insights of protein structural rearrangements required to accommodate the heme-Fe(III) upon ibuprofen and warfarin binding. In the absence of drugs, the heme-Fe(III) atom is penta-coordinated having distorted 4+1 configuration made by the nitrogen atoms of the porphyrin ring and the oxygen phenoxy atom of the Tyr161 residue. MD simulations show that ibuprofen and warfarin association to the secondary fatty acid (FA) binding site 2 (FA2) induces a reorientation of domain I of HSA-heme-Fe(III), this leads to the redirection of the His146 residue providing an additional bond to the heme-Fe(III) atom, providing the 5+1 configuration. The comparison of Fe-K edge XANES spectra calculated using MD structures with those obtained experimentally confirms the reliability of the proposed structural model. As a whole, combining XAS and MD simulations it has been possible to provide a reliable model of the heme-Fe(III) atom coordination state and to understand the complex allosteric transition occurring in HSA-heme-Fe(III) upon ibuprofen and warfarin binding.
authors.affiliation: Department of Sciences, Roma Tre University, Roma, Italy.
authors.forename: Carlo
authors.initials: C
authors.lastname: Meneghini
authors.affiliation: Department of Sciences, Roma Tre University, Roma, Italy; National Institute of Biostructures and Biosystems, Roma, Italy.
authors.forename: Loris
authors.initials: L
authors.lastname: Leboffe
authors.affiliation: Department of Sciences, Roma Tre University, Roma, Italy.
authors.forename: Monica
authors.initials: M
authors.lastname: Bionducci
authors.affiliation: Biomedical Research Division, Department of Theoretical and Applied Sciences, and Center of Neuroscience, University of Insubria, Busto Arsizio (VA), Italy.
authors.forename: Gabriella
authors.initials: G
authors.lastname: Fanali
authors.affiliation: Institute for Molecular Recognition Chemistry, National Research Council, Milano, Italy.
authors.forename: Massimiliano
authors.initials: M
authors.lastname: Meli
authors.affiliation: Institute for Molecular Recognition Chemistry, National Research Council, Milano, Italy.
authors.forename: Giorgio
authors.initials: G
authors.lastname: Colombo
authors.affiliation: Biomedical Research Division, Department of Theoretical and Applied Sciences, and Center of Neuroscience, University of Insubria, Busto Arsizio (VA), Italy.
authors.forename: Mauro
authors.initials: M
authors.lastname: Fasano
authors.affiliation: National Institute of Biostructures and Biosystems, Roma, Italy; Interdepartmental Laboratory of Electron Microscopy, Roma Tre University, Roma, Italy.
authors.forename: Paolo
authors.initials: P
authors.lastname: Ascenzi
authors.affiliation: Department of Sciences, Roma Tre University, Roma, Italy.
authors.forename: Settimio
authors.initials: S
authors.lastname: Mobilio
mesh_terms: D015502:Absorptiometry, Photon; D000494:Allosteric Regulation / Q000187:drug effects; D006418:Heme / Q000737:chemistry*; D006801:Humans; D007052:Ibuprofen / Q000737:chemistry* / Q000494:pharmacology; D007501:Iron / Q000737:chemistry*; D008958:Models, Molecular; D008968:Molecular Conformation; D056004:Molecular Dynamics Simulation; D012709:Serum Albumin / Q000737:chemistry*; D014859:Warfarin / Q000737:chemistry* / Q000494:pharmacology
chemical_list: D012709:Serum Albumin; D006418:Heme; D014859:Warfarin; D007501:Iron; D007052:Ibuprofen