Electron paramagnetic resonance study on calmodulin: conformational change and interaction with divalent cations |
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Authors: | Y.H. Xü K. Gietzen H.-J. Galla |
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Affiliation: | 1. Department of Biophysics, University of Ulm, Oberer Eselsberg, D-7900 Ulm, FRG;2. Department of Pharmacology and Toxicology, University of Ulm, Oberer Eselsberg, D-7900 Ulm, FRG |
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Abstract: | Biologically active spin labelled derivatives of calmodulin were prepared and used to study CA2+- and Mg2+-induced conformational changes of the protein. The rotational correlation time of the spin labelled residues increased upon addition of divalent cations. Two calcium ions per spin labelled calmodulin were found to induce a 75% conformational change, whereas four calcium ions were necessary for a maximum conformational change. The increase in rotational correlation time induced by Mg2+ is less pronounced. Two different covalently attached spin labels (iodoacetamide and maleimide) were compared and marked differences were found in their chemical stability. The binding of manganese ions to calmodulin could be observed directly from the electron paramagnetic resonance spectra of these paramagnetic ions. Two specific classes of binding sites, each binding two manganese ions with , respectively, were determined. Further ion binding occurs at non-specific sites. |
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Keywords: | Proteins calmodulin spin label divalent ions conformational change electron paramagnetic resonance |
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