Ca2+/Mg2+ exchange in parvalbumin and other EF-hand proteins.: A theoretical study
Ca2+/Mg2+ exchange in parvalbumin and other EF-hand proteins.: A theoretical study
复制标题
DOI：
10.1006/jmbi.1998.2329
复制
发表时间：
1999-01-15
影响因子：
5.6
通讯作者：
Sanejouand, YH
中科院分区：
文献类型：
--
作者：
Allouche, D;Parello, J;Sanejouand, YH
一个显着的构象重排发生后，Ca 2 +/Mg 2+交换的C-末端EF-手网站（标记网站EF或EF-4）的小白蛋白，最初建立的X-射线晶体学。这种构象重排的特征如下：（i）配位数从Ca-负载形式的7个氧原子减少到Mg-负载形式的6个氧原子，Ca ~（2+）的七配位对应于7个氧原子的斜五角双锥构型，而Mg ~（2+）的六配位对应于6个氧原子的正八面体构型;和（ii）在EF-手环序列的相对位置12处的Glu 101（标记为“Glu 12”）在Ca-负载形式中作为二齿配体，在Mg-负载形式中作为单齿配体。作为构象重排的一部分，当Ca ~（2+）被Mg ~（2+）取代时，二面角经历一个从左（+）到左（-）的转变，而X（2）角实际上保持不变，两种形式的X（3）角采用几乎镜像的关系。为了理解这种构象重排的分子机制，我们使用自由能微扰（FEP）方法进行了理论研究，从同一小清蛋白的高分辨率晶体结构开始（pike 4.10同种型），不同之处在于它们的两个阳离子位点EF-3（或CD）和EF-4（或EF）的取代，即EF-3（Ca ~（2+））和EF-4（Ca ~（2+））的1 pal结构，EF-3（Ca ~（2+））和EF-1（Mg ~（2+））的4pal结构。当Mg ~（2+）在4pal的EF-4位点“炼金术”地转化为Ca ~（2+）时，FEP计算正确地预测了Glu ~（12）的构象重排。当Ca 2+在4pal的EF-3位点内转化为Mg 2+时，FEP计算预测了目前没有晶体学数据的完全Mg负载形式的拓扑结构。正如预期的那样，Glu 62（在EF-3环中的相对位置12处）被预测为在Mg 2+周围的六个氧原子的规则八面体排列内的单齿残基。我们还研究了其他两个典型的EF-手蛋白，肌钙蛋白C（TnC）和钙调蛋白（CaM），其中没有三维结构的镁负载形式是迄今为止的钙/镁交换过程中的行为。它也被预测，EF-3网站的TnC和EF-1网站的CaM有其不变的Glu 12残基切换从双齿的单齿构型时，Ca 2+被Mg 2+取代，与六个氧原子被观察到的配位球的炼金术产生的Mg 2+阳离子。(C)北京：科学出版社.
A remarkable conformational rearrangement occurs upon Ca2+/Mg2+ exchange in the C-terminal EF-hand site (labelled site EF or EF-4) of parvalbumin, as initially established by X-ray crystallography. Such a conformational rearrangement is characterised as follows: (i) the co-ordination number decreases from seven oxygen atoms in the Ca-loaded form to six oxygen atoms in the Mg-loaded form, the heptaco-ordination of Ca2+ corresponding with a skewed pentagonal bipyramid configuration of the seven oxygen atoms, whereas the hexaco-ordination of Mg2+ corresponds with a regular octahedral configuration of the six oxygen atoms; and (ii) Glu101, at the relative position 12 in the EF-hand loop sequence (labelled "Glu12"), acts as a bidentate ligand in the Ca-loaded form and as a monodentate ligand in the Mg-loaded form. As part of the conformational rearrangement, the :!, dihedral angle undergoes a gauche(+) to gauche(-) transition upon substitution of Ca2+ by Mg2+, whereas the chi(2) angle remains practically unchanged and the chi(3) angles in both forms adopt a nearly mirror image relationship. In order to understand the molecular mechanisms underlying such a conformational rearrangement,we undertook a theoretical study using the free energy perturbation (FEP) method, starting from high-resolution crystal structures of the same parvalbumin (pike 4.10 isoform) differing by the substitution of their two cationic sites EF-3 (or CD) and EF-4 (or EF), i.e. the 1pal structure with EF-3(Ca2+) and EF-4(Ca2+), the 4pal structure with EF-3(Ca2+) and EF-I(Mg2+). When Mg2+ is "alchemically" transformed into Ca2+ within the EF-4 site of 4pal, the conformational rearrangement of Glu12 is correctly predicted by the FEP calculation. When Ca2+ is transformed into Mg2+ within the EF-3 site of 4pal, the FEP calculation predicts the topology of the fully Mg-loaded form for which no crystallographic data is presently available. As expected, Glu62 (at the relative position 12 in EF-3 loop) is predicted to be a monodentate residue within a regular octahedral arrangement of six oxygen atoms around Mg2+. We also investigated the behaviour during Ca2+/Mg2+ exchange of two other typical EF-hand proteins, troponin C (TnC) and calmodulin (CaM), for which no three-dimensional structure of their Mg-loaded forms is available so far. It is also predicted that the EF-3 site of TnC and the EF-1 site of CaM have their invariant Glu12 residues switching from the bidentate to the monodentate configuration when Ca2+ is substituted by Mg2+, with six oxygen atoms being observed in the co-ordination sphere of the alchemically generated Mg2+ cation. (C) 1999 Academic Press.