@article{open1687,
          volume = {19},
          number = {6},
           month = {August},
          author = {Sandeep Kumar and Deepak Sharma and Rajesh Kumar and Rajesh Kumar},
            note = {Copyright of this article belongs to Springer.},
           title = {Electrostatic effects control the stability and iron release kinetics of ovotransferrin.},
       publisher = {Springer},
            year = {2014},
         journal = {Journal of biological inorganic chemistry},
           pages = {1009--24},
        keywords = {Iron release; Electrostatic interactions; Anion-binding Conformational change; Structural stability},
             url = {http://crdd.osdd.net/open/1687/},
        abstract = {The contribution of electrostatic interactions to the stability of ovotransferrin-Fe(3+) (oTf-Fe(3+)) complex has been assessed by equilibrium experiments that measure iron retention level of diferric-ovotransferrin (Fe2oTf) as a function of pH and urea in the presence of salts (NaCl, Na2SO4, NaBr, NaNO3) and sucrose at 25 ?C. As [salt] is increased, the pH-midpoint for iron release increases monoexponentially and plateau at {\texttt{\char126}}0.4({$\pm$}0.05) M NaCl/NaBr/NaNO3 or {\texttt{\char126}}0.15({$\pm$}0.03) M Na2SO4. However, at pH 7.4, the urea-midpoints for iron release (based on fluorescence emission at 340 nm) and for unfolding of Fe2oTf and apo-ovotransferrin (based on ellipticity values at 222 and 282 nm) decrease at low salt concentrations [{$\leq$}0.1({$\pm$}0.02) M Na2SO4 or {$\leq$}0.35({$\pm$}0.15) M NaCl], but increase at higher salt concentrations. Furthermore, Na2SO4 has a greater effect than NaCl in increasing the urea-midpoints for iron release and unfolding. These results indicate that at low salt concentrations, the electrostatic effects destabilize the oTf-Fe(3+) complex and also decrease the structural stability of the proteins. In contrast, at higher concentrations, salt ions behave according to Hofmeister series. At pH 5.6, as [salt] is increased, the rate constants for reductive iron release (Fe(2+) release) and urea denaturation-induced iron release (Fe(3+) release) from the N-lobe of oTf (FeNoTf) increase monoexponentially and plateau at {\texttt{\char126}}0.4({$\pm$}0.1) M NaNO3/NaCl or {\texttt{\char126}}0.2({$\pm$}0.05) M Na2SO4. These results suggest that the anion-binding-induced conformational change as well as the electrostatic screening of surface Coulombic interactions plays important role in accelerating the iron release from FeNoTf under endosomal pH conditions.}
}