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首页> 外文期刊>Journal of biological inorganic chemistry: JBIC: a publication of the Society of Biological Inorganic Chemistry >Electrostatic effects control the stability and iron release kinetics of ovotransferrin
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Electrostatic effects control the stability and iron release kinetics of ovotransferrin

机译：静电作用控制着卵转铁蛋白的稳定性和铁释放动力学

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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 (Fe_2oTf) as a function of pH and urea in the presence of salts (NaCl,Na_2SO_4, NaBr, NaNO_3) and sucrose at 25 ℃. As [salt] is increased, the pH-midpoint for iron release increases monoexponentially and plateau at ~0.4(±0.05) M NaCl/NaBr/NaNO_3 or ~0.15(±0.03) M Na_2SO_4. However, at pH 7.4, the urea-midpoints for iron release (based on fluorescence emission at 340 nm) and for unfolding of Fe_2oTf and apo-ovotransferrin (based on ellipticity values at 222 and 282 nm) decrease at low salt concentrations [B0.1(±0.02) M Na_2SO_4 or B0.35(±0.15) M NaCl], but increase at higher salt concentrations. Furthermore, Na_2SO_4 has a greater effect than NaCl in increasing the ureamidpoints 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 NaNO_3/NaCl or~0.2(±0.05) M Na_2SO_4. These results suggest that the anion-bindinginduced 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.
机译：静电相互作用对卵转铁蛋白-Fe〜（3+）（oTf​​-Fe〜（3+））配合物的稳定性的贡献已通过平衡实验进行了评估，该平衡实验测量了二铁-卵转铁蛋白（Fe_2oTf）的铁保留水平是Fe的函数。在25℃下存在盐（NaCl，Na_2SO_4，NaBr，NaNO_3）和蔗糖的条件下pH和尿素。随着[盐]的增加，铁释放的pH中点呈单指数增加，并在〜0.4（±0.05）M NaCl / NaBr / NaNO_3或〜0.15（±0.03）M Na_2SO_4处稳定。但是，在pH 7.4时，低盐浓度下铁释放（基于340 nm的荧光发射）以及Fe_2oTf和载脂蛋白转铁蛋白解折叠（基于222和282 nm的椭圆率值）的尿素中点降低[B0。 1（±0.02）M Na_2SO_4或B0.35（±0.15）M NaCl]，但在较高的盐浓度下会增加。此外，Na_2SO_4在增加铁释放和展开的脲中点方面比NaCl具有更大的作用。这些结果表明，在低盐浓度下，静电作用使oTf-Fe〜（3+）络合物不稳定，并降低了蛋白质的结构稳定性。相反，在较高浓度下，盐离子的行为符合霍夫迈斯特系列。在pH 5.6下，随着[盐]的增加，oTf的N瓣中还原性铁释放（Fe〜（2+）释放）和尿素变性诱导的铁释放（Fe〜（3+）释放）的速率常数（FeNoTf）呈单指数增加，并在〜0.4（±0.1）M NaNO_3 / NaCl或〜0.2（±0.05）M Na_2SO_4处稳定。这些结果表明，在内体pH条件下，阴离子结合诱导的构象变化以及表面库仑相互作用的静电筛选在加速FeNoTf中铁的释放中起着重要作用。

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