Mechanism of Zn<sup>2+</sup> and Ca<sup>2+</sup> Binding to Human S100A1
2021
Viktoriia E. Baksheeva | Andrei Yu. Roman | Claude Villard | François Devred | Deborah Byrne | Dahbia Yatoui | Arthur O. Zalevsky | Alisa A. Vologzhannikova | Andrey S. Sokolov | Sergei E. Permyakov | Andrey V. Golovin | Gary S. Shaw | Philipp O. Tsvetkov | Evgeni Yu. Zernii
S100A1 is a member of the S100 family of small ubiquitous Ca<sup>2+</sup>-binding proteins, which participates in the regulation of cell differentiation, motility, and survival. It exists as homo- or heterodimers. S100A1 has also been shown to bind Zn<sup>2+</sup>, but the molecular mechanisms of this binding are not yet known. In this work, using ESI-MS and ITC, we demonstrate that S100A1 can coordinate 4 zinc ions per monomer, with two high affinity (K<sub>D</sub>~4 and 770 nm) and two low affinity sites. Using competitive binding experiments between Ca<sup>2+</sup> and Zn<sup>2+</sup> and QM/MM molecular modeling we conclude that Zn<sup>2+</sup> high affinity sites are located in the EF-hand motifs of S100A1. In addition, two lower affinity sites can bind Zn<sup>2+</sup> even when the EF-hands are saturated by Ca<sup>2+</sup>, resulting in a 2Ca<sup>2+</sup>:S100A1:2Zn<sup>2+</sup> conformer. Finally, we show that, in contrast to calcium, an excess of Zn<sup>2+</sup> produces a destabilizing effect on S100A1 structure and leads to its aggregation. We also determined a higher affinity to Ca<sup>2+</sup> (K<sub>D</sub>~0.16 and 24 μm) than was previously reported for S100A1, which would allow this protein to function as a Ca<sup>2+</sup>/Zn<sup>2+</sup>-sensor both inside and outside cells, participating in diverse signaling pathways under normal and pathological conditions.
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