Mittl Peer R E, Fritz Günter, Sargent David F, Richmond Timothy J, Heizmann Claus W, Grütter Markus G
Institute of Biochemistry, University of Zurich, Winterthurer Strasse 190, 8057 Zürich, Switzerland.
Acta Crystallogr D Biol Crystallogr. 2002 Aug;58(Pt 8):1255-61. doi: 10.1107/s0907444902008430. Epub 2002 Jul 20.
S100 proteins are involved in metal-dependent intracellular signalling. Metal-free S100A3, a cysteine-rich Ca(2+)- and Zn(2+)-binding protein, has been crystallized by vapour diffusion under the strict exclusion of oxygen and in the absence of divalent metal ions. Metal binding induces large conformational changes, rendering the apo-S100A3 crystals very sensitive to various metal compounds. Therefore, the structure was solved by MIRAS phasing using potassium iodide and xenon derivatives. Iodide replaces a water molecule at the surface of the S100A3 protein, whereas xenon binds in a hydrophobic cavity at the dimer interface. Despite significant non-isomorphism, the combination of both derivatives was sufficient for structure determination. The overall apo-S100A3 structure resembles the structures of metal-free S100B and S100A6 solution structures. In contrast to the NMR structures, the EF-hand loops are well ordered in the apo-S100A3 crystal structure. In the N-terminal pseudo-EF-hand loop a water molecule occupies the position of the Ca(2+) ion. The C-terminal canonical EF-hand loop shows an extended conformation and a different helix arrangement to other S100/metal complex crystal structures.
S100蛋白参与金属依赖性细胞内信号传导。无金属的S100A3是一种富含半胱氨酸的钙和锌结合蛋白，已通过气相扩散在严格排除氧气且不存在二价金属离子的条件下结晶。金属结合会引起较大的构象变化，使无载脂蛋白S100A3晶体对各种金属化合物非常敏感。因此，该结构通过使用碘化钾和氙衍生物的MIRAS相位法解析。碘取代了S100A3蛋白表面的一个水分子，而氙则结合在二聚体界面的一个疏水腔内。尽管存在明显的非同晶性，但两种衍生物的组合足以确定结构。无载脂蛋白S100A3的整体结构类似于无金属的S100B和S100A6溶液结构。与核磁共振结构不同，EF手环在无载脂蛋白S100A3晶体结构中排列良好。在N端假EF手环中，一个水分子占据了钙离子的位置。C端典型EF手环显示出伸展构象，且与其他S100/金属复合物晶体结构的螺旋排列不同。
