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Biophys. J. BioFAST: First Published January 5, 2007. doi:10.1529/biophysj.106.094284
© 2007 by the Biophysical Society.

A more recent version of this article appeared on March 15, 2007.
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PROTEINS

Electrostatic interactions modulate the conformation of collagen I

Uwe Freudenberg 1, Sven Holger Behrens 2, Petra Welzel 1, Martin Müller 3, Milauscha Grimmer 1, Katrin Salchert 1, Tilman Taeger 2, Kati Schmidt 2, Wolfgang Pompe 4 and Carsten Werner 1*

1 Leibniz Institute of Polymer Research Dresden, Max Bergmann Center of Biomaterials Dresden
2 BASF Aktiengesellschaft, 67056 Ludwigshafen, Germany
3 Leibniz Institute of Polymer Research Dresden
4 Technische Universitat Dresden, Department of Materials Science,Max Bergmann Center of Biomaterials

* To whom correspondence should be addressed. E-mail: werner{at}ipfdd.de.

Submitted on August 1, 2006
Revised on August 30, 2006
Accepted on 1 December 2006


  Abstract
The pH and electrolyte dependent charging of collagen I fibrils was analyzed by streaming potential/ streaming current experiments using the Microslit Electrokinetic Setup (MES). Differential scanning calorimetry (DSC) and circular dichroism spectroscopy (CD) were applied in similar electrolyte solutions to characterize the influence of electrostatic interactions on the conformational stability of the protein. The acid base behavior of collagen I was found to be strongly influenced by the ionic strength in KCl as well as in CaCl2 solutions. An increase of the ionic strength with KCl from 10-4 M to 10-2 M shifts the isoelectric point (IEP) of the protein from pH 7.5 to 5.3. However, a similar increase of the ionic strength in CaCl2 solutions shifts the IEP from 7.5 to above pH 9. Enhanced thermal stability with increasing ionic strength was observed by DSC in both electrolyte systems. In line with this, CD results show an increase of the helicity with increasing ionic strength. Better screening of charged residues and the formation of salt bridges are assumed to cause the stabilization of collagen I with increasing ionic strength in both electrolyte systems. Preferential adsorption of hydroxide ions onto intrinsically uncharged sites in KCl solutions and calcium binding to negatively charged carboxylic acid moieties in CaCl2 solutions are concluded to shift the IEP and influence the conformational stability of the protein.

Key Words: DSC, charge characterization, circular dichroism spectroscopy, electrokinetic measurements, ion adsorption, thermal stability






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Copyright © 2007 by the Biophysical Society.