title: Characterization of chromodulin by X-ray absorption and electron paramagnetic resonance spectroscopies and magnetic susceptibility measurements.
abstract: The biologically active form of the essential trace element chromium is believed to be the oligopeptide chromodulin. Chromodulin binds four chromic ions before binding at or near the active site of activating insulin receptor and subsequently potentiating the tyrosine kinase activity of the receptor. Charge balance arguments and preliminary spectroscopic studies suggested that the chromic centers might be part of a multinuclear assembly. Using a combination of X-ray absorption and electron paramagnetic resonance spectroscopies and variable-temperature magnetic susceptibility measurements, we found that holochromodulin is shown to possess an antiferromagnetically coupled trinuclear assembly which probably weakly interacts with a fourth chromium center. The chromium centers possess octahedron coordination comprised of oxygen-based ligation, presumably derived primarily from oligopeptide-supplied carboxylate groups. X-ray absorption data cannot be reproduced with the presence of sulfur atom(s), indicating that the cysteine thiolate group does not coordinate to the chromium centers. Thus, chromodulin possesses a unique type of multinuclear assembly, distinct from those known in other bioinorganic systems.
authors.affiliation: Department of Applied Science, University of California, Davis 95616, USA.
authors.forename: Lilian
authors.initials: L
authors.lastname: Jacquamet
authors.forename: Yanjie
authors.initials: Y
authors.lastname: Sun
authors.forename: Jason
authors.initials: J
authors.lastname: Hatfield
authors.forename: Weiwei
authors.initials: W
authors.lastname: Gu
authors.forename: Stephen P
authors.initials: SP
authors.lastname: Cramer
authors.forename: Michael W
authors.initials: MW
authors.lastname: Crowder
authors.forename: Gary A
authors.initials: GA
authors.lastname: Lorigan
authors.forename: John B
authors.initials: JB
authors.lastname: Vincent
authors.forename: Jean-Marc
authors.initials: JM
authors.lastname: Latour
mesh_terms: D002352:Carrier Proteins / Q000737:chemistry*; D002857:Chromium / Q000737:chemistry; D004578:Electron Spin Resonance Spectroscopy / Q000379:methods; D008280:Magnetics; D013052:Spectrometry, X-Ray Emission / Q000379:methods
chemical_list: D002352:Carrier Proteins; C406742:chromodulin protein, mouse; D002857:Chromium