Ostendorp Thorsten, Diez Joachim, Heizmann Claus W, Fritz Günter
Fachbereich Biologie, Mathematisch-Naturwissenschaftliche Sektion, Universität Konstanz, 78459 Konstanz, Germany.
Biochim Biophys Acta. 2011 May;1813(5):1083-91. doi: 10.1016/j.bbamcr.2010.10.006. Epub 2010 Oct 13.
S100B is a homodimeric zinc-, copper-, and calcium-binding protein of the family of EF-hand S100 proteins. Zn(2+) binding to S100B increases its affinity towards Ca(2+) as well as towards target peptides and proteins. Cu(2+) and Zn(2+) bind presumably to the same site in S100B. We determined the structures of human Zn(2+)- and Ca(2+)-loaded S100B at pH 6.5, pH 9, and pH 10 by X-ray crystallography at 1.5, 1.4, and 1.65Å resolution, respectively. Two Zn(2+) ions are coordinated tetrahedrally at the dimer interface by His and Glu residues from both subunits. The crystal structures revealed that ligand swapping occurs for one of the four ligands in the Zn(2+)-binding sites. Whereas at pH 9, the Zn(2+) ions are coordinated by His15, His25, His 85', and His 90', at pH 6.5 and pH 10, His90' is replaced by Glu89'. The results document that the Zn(2+)-binding sites are flexible to accommodate other metal ions such as Cu(2+). Moreover, we characterized the structural changes upon Zn(2+) binding, which might lead to increased affinity towards Ca(2+) as well as towards target proteins. We observed that in Zn(2+)-Ca(2+)-loaded S100B the C-termini of helix IV adopt a distinct conformation. Zn(2+) binding induces a repositioning of residues Phe87 and Phe88, which are involved in target protein binding. This article is part of a Special Issue entitled: 11th European Symposium on Calcium.
S100B是EF手型S100蛋白家族中的一种同二聚体锌、铜和钙结合蛋白。锌离子（Zn(2+)）与S100B结合会增加其对钙离子（Ca(2+)）以及靶肽和蛋白质的亲和力。铜离子（Cu(2+)）和锌离子可能结合到S100B中的同一位点。我们分别通过X射线晶体学在1.5埃、1.4埃和1.65埃分辨率下测定了在pH 6.5、pH 9和pH 10时人源锌离子和钙离子负载的S100B的结构。两个锌离子在二聚体界面通过两个亚基的组氨酸和谷氨酸残基以四面体方式配位。晶体结构表明，锌离子结合位点中的四个配体之一发生了配体交换。在pH 9时，锌离子由His15、His25、His 85'和His 90'配位，而在pH 6.5和pH 10时，His90'被Glu89'取代。结果表明，锌离子结合位点具有灵活性，可容纳其他金属离子如铜离子。此外，我们对锌离子结合后的结构变化进行了表征，这可能导致对钙离子以及靶蛋白的亲和力增加。我们观察到，在锌离子和钙离子负载的S100B中，螺旋IV的C末端呈现出独特的构象。锌离子结合诱导了参与靶蛋白结合的Phe87和Phe88残基的重新定位。本文是名为：第11届欧洲钙研讨会的特刊的一部分。
