Mercury(II) Binding to Metallothionein in Mytilus edulis revealed by High Energy-Resolution XANES Spectroscopy

Abstract : Of all divalent metals, mercury (Hg(II)) has the highest affinity for metallothioneins. Hg(II) is considered to be enclosed in the  and  domains as tetrahedral -type Hg4Cys11-12 and -type Hg3Cys9 clusters similarly to Cd(II) and Zn(II). However, neither the four-fold coordination of Hg nor the existence of Hg-Hg atomic pairs have ever been demonstrated, and the Hg(II) partitioning among the two protein domains is unknown. Using high energy-resolution XANES spectroscopy, MP2 geometry optimization, and biochemical analysis, we provide evidence for the coexistence of two-coordinate Hg-thiolate complex and four-coordinate Hg-thiolate cluster with a metacinnabar-type (β-HgS) structure in the α domain of separate metallothionein molecules from blue mussel under in vivo exposure. The findings suggest that the CXXC claw setting of thiolate donors, which only exists in the  domain, acts as a nucleation center for the polynuclear complex and that the five CXC motifs from this domain serve as the cluster-forming motifs. Oligomerization is driven by metallophilic Hg-Hg interactions. Our results provide clues as to why Hg has higher 2 affinity for the  than the  domain. More generally, they provide a foundation for understanding how metallothioneins mediate mercury detoxification in the cell under in vivo conditions.
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Alain Manceau, Paco Bustamante, Ahmed Haouz, Jean Paul Bourdineaud, Maria Gonzalez-Rey, et al.. Mercury(II) Binding to Metallothionein in Mytilus edulis revealed by High Energy-Resolution XANES Spectroscopy. Chemistry - A European Journal, Wiley-VCH Verlag, 2019, 25 (4), pp.997-1009. ⟨10.1002/chem.201804209⟩. ⟨hal-02314780⟩

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