Quanten Thomas, De Mayaer Tessa, Shestakova Pavletta, Parac-Vogt Tatjana N
Laboratory of Bio-Inorganic Chemistry, Department of Chemistry, KU Leuven, Leuven, Belgium.
NMR Centre, Institute of Organic Chemistry with Centre of Phytochemistry, Bulgarian Academy of Sciences, Sofia, Bulgaria.
Front Chem. 2018 Aug 28;6:372. doi: 10.3389/fchem.2018.00372. eCollection 2018.
In this paper we investigate the effect of three different types of surfactants, on the hydrolysis of Cytochrome c (Cyt c), a predominantly α helical protein containing a heme group, promoted by [Ce(α PW)2]10- (CeK) and [Zr(α PW)2]10- (ZrK) polyoxometalates. In the presence of SDS, Zw3 12, or CHAPS surfactants, which are commonly used for solubilizing hydrophobic proteins, the specificity of CeK or ZrK toward hydrolysis of Cyt c does not change. However, the hydrolysis rate of Cyt c by CeK was increased in the presence of SDS, but decreased in the presence of CHAPS, and was nearly inhibited in the presence of Zw3 12. The Circular dichroism and Tryptophan fluorescence spectroscopy have shown that the structural changes in Cyt c caused by surfactants are similar to those caused by POMs, hence the same specificity in the absence or presence of surfactants was observed. The results also indicate that for Cyt c hydrolysis to occur, large unfolding of the protein is needed in order to accommodate the POMs. While SDS readily unfolds Cyt c, the protein remains largely folded in the presence of CHAPS and Zw3 12. Addition of POMs to Cyt c solutions in CHAPS results in unfolding of the structure allowing the interaction with POMs to occur and results in protein hydrolysis. Zw3 12, however, locks Cyt c in a conformation that resists unfolding upon addition of POM, and therefore results in nearly complete inhibition of protein hydrolysis.
在本文中，我们研究了三种不同类型的表面活性剂对细胞色素c（Cyt c）水解的影响。细胞色素c是一种主要含α螺旋且含有血红素基团的蛋白质，其水解由[Ce(α PW)2]10-（CeK）和[Zr(α PW)2]10-（ZrK）多金属氧酸盐促进。在常用于增溶疏水蛋白质的十二烷基硫酸钠（SDS）、十二烷基三甲基溴化铵（Zw3 12）或3-[(3-胆酰胺丙基)二甲基铵]-1-丙磺酸（CHAPS）表面活性剂存在的情况下，CeK或ZrK对Cyt c水解的特异性不变。然而，在SDS存在下，CeK对Cyt c的水解速率增加，但在CHAPS存在下降低，在Zw3 12存在下几乎受到抑制。圆二色光谱和色氨酸荧光光谱表明，表面活性剂引起的Cyt c结构变化与多金属氧酸盐引起的相似，因此在有无表面活性剂的情况下都观察到相同的特异性。结果还表明，为了使Cyt c发生水解，需要蛋白质大量展开以容纳多金属氧酸盐。虽然SDS能使Cyt c容易展开，但在CHAPS和Zw3 12存在下蛋白质仍基本保持折叠状态。向CHAPS中的Cyt c溶液中添加多金属氧酸盐会导致结构展开，从而允许与多金属氧酸盐发生相互作用并导致蛋白质水解。然而，Zw3 12将Cyt c锁定在一种构象中，该构象在添加多金属氧酸盐时抵抗展开，因此导致蛋白质水解几乎完全受到抑制。
