Institut de Neurophysiopathologie, INP, CNRS, Faculté des Sciences Médicales et Paramédicales, Aix-Marseille Université, 13005 Marseille, France.
Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, 119992 Moscow, Russia.
Biomolecules. 2021 Dec 3;11(12):1823. doi: 10.3390/biom11121823.
S100A1 is a member of the S100 family of small ubiquitous Ca-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, 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 (K4 and 770 nm) and two low affinity sites. Using competitive binding experiments between Ca and Zn and QM/MM molecular modeling we conclude that Zn high affinity sites are located in the EF-hand motifs of S100A1. In addition, two lower affinity sites can bind Zn even when the EF-hands are saturated by Ca, resulting in a 2Ca:S100A1:2Zn conformer. Finally, we show that, in contrast to calcium, an excess of Zn produces a destabilizing effect on S100A1 structure and leads to its aggregation. We also determined a higher affinity to Ca (K0.16 and 24 μm) than was previously reported for S100A1, which would allow this protein to function as a Ca/Zn-sensor both inside and outside cells, participating in diverse signaling pathways under normal and pathological conditions.
S100A1 是 S100 家族中小而普遍存在的 Ca 结合蛋白家族的成员，它参与细胞分化、运动和存活的调节。它以同二聚体或异二聚体的形式存在。S100A1 也被证明可以结合 Zn，但这种结合的分子机制尚不清楚。在这项工作中，我们使用 ESI-MS 和 ITC 证明 S100A1 可以每个单体协调 4 个锌离子，其中 2 个具有高亲和力（K4 和 770nm），2 个具有低亲和力。通过 Ca 和 Zn 之间的竞争性结合实验和 QM/MM 分子建模，我们得出结论，Zn 的高亲和力位点位于 S100A1 的 EF 手基序中。此外，即使 EF 手被 Ca 饱和，两个较低亲和力的位点也可以结合 Zn，从而形成 2Ca:S100A1:2Zn 构象。最后，我们表明，与钙相反，过量的锌会对 S100A1 结构产生不稳定的影响，并导致其聚集。我们还确定了对 Ca 的更高亲和力（K0.16 和 24μm），高于之前报道的 S100A1，这将使该蛋白能够在细胞内外作为 Ca/Zn 传感器发挥作用，参与正常和病理条件下的多种信号通路。
