creators_name: Kumar, Sandeep
creators_name: Sharma, Deepak
creators_name: Kumar, Rajesh
creators_name: Kumar, Rajesh
type: article
datestamp: 2015-07-20 04:47:12
lastmod: 2015-07-20 04:47:12
metadata_visibility: show
title: Electrostatic effects control the stability and iron release kinetics of ovotransferrin.
ispublished: pub
subjects: QR
keywords: Iron release; Electrostatic interactions; Anion-binding Conformational change; Structural stability
note: Copyright of this article belongs to Springer.
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 ~0.4(±0.05) M NaCl/NaBr/NaNO3 or ~0.15(±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 [≤0.1(±0.02) M Na2SO4 or ≤0.35(±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 ~0.4(±0.1) M NaNO3/NaCl or ~0.2(±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.
date: 2014-08
date_type: published
publication: Journal of biological inorganic chemistry
volume: 19
number: 6
publisher: Springer
pagerange: 1009-24
refereed: TRUE
issn: 1432-1327
official_url: http://link.springer.com/article/10.1007%2Fs00775-014-1145-2
citation:   Kumar, Sandeep and Sharma, Deepak and Kumar, Rajesh and Kumar, Rajesh  (2014) Electrostatic effects control the stability and iron release kinetics of ovotransferrin.  Journal of biological inorganic chemistry, 19 (6).  pp. 1009-24.  ISSN 1432-1327