Shape and Stability of Fibronectin in Solutions of Different pH and Ionic Strength

Publisher Website
Google Scholar
Abstract
At low ionic strength (0.05 M) the sedimentation coefficient of monomeric [human] plasma fibronectin varied from 8S, at pH 3 and 11, to 13.5S at neutral pH. The lower s20,w value indicates a stretched arrangement of the 2 arms of the molecule which was observed in most EM studies. The higher value is consistent with a still very asymmetric but more condensed shape, which is probably brought about by backfolding and interactions between chain segments of different net charge. A model of this internal association is based on the finding that segments of rather different isoelectric points alternate along the fibronectin chains. A similar pH dependence was observed for a 140-kDa [kilodalton] fragment from the middle region of fibronectin which carries segments of low and high isoelectric points at its ends. At high ionic strength (0.35 M) the pH dependence of the sedimentation coefficients was less pronounced and intermediate s20,w values were found. This is expected when both repulsive and attractive interactions are weakened by the electrolyte. It was verified by circular dichroism spectra that the protein was not denatured at pH 3 or 11. Thermal transition curves revealed a destabilization at pH 3 but the thermal denaturation occurred well above 20.degree. C at which the pH dependence of the solution shape was studied.

This publication has 48 references indexed in Scilit: