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 α and β domains as tetrahedral α‐type Hg 4 Cys 11‐12 and β‐type Hg 3 Cys 9 clusters similar 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, 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 is provided. The findings suggest that the CXXC claw setting of thiolate donors, which only exists in the α 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 affinity for the α than the β domain. More generally, this work provides a foundation for understanding how metallothioneins mediate mercury detoxification in the cell under in vivo conditions.

The chemical species of mercury accumulated by Pseudomonas idrijaensis, a bacterium from a rock of the Idrija mercury mine, Slovenia.

“…2b). This Hg coordination effect, described previously with a comparison of the Hg(Cys) 2 , Hg(D-penicillamin) 3 , and Hg(Cys) 4 HR-XANES spectra (Manceau et al, 2019), is explained physically by the Natoli rule (Bianconi et al, 1983). The distinctive difference of Pi-4-Intra is better seen in its comparison with Pi-4-Tot (Fig.…”

“…The four HR-XANES spectra feature a near-edge peak at 12279.3 eV (indicator region "A" in Fig. 2a) characteristic of linear dithiolate complex (Hg(SR) 2 ) (Manceau et al, 2019). The straighter the RS-Hg-SR angle, the sharper is this peak.…”

“…Mercury L 3 -edge high energy-resolution XANES (HR-XANES) spectra were measured at 10-15 K with high-reflectivity analyzer crystals (Rovezzi et al, 2017) on beamline ID26 at the European Synchrotron Radiation Facility (ESRF). Data were analyzed against a large database of spectra for mercury minerals (α-HgS, β-HgS, β-HgS NP ), Hg(II) complexes in natural organic matter, and Hg(II) and methylmercury (MeHg) model complexes with thiolate ligands (Manceau et al, 2015a(Manceau et al, , 2015b(Manceau et al, , 2016(Manceau et al, , 2018(Manceau et al, , 2019Bourdineaud et al, 2019). All reference spectra were considered as a basis for identification, but only diagnostic spectra are discussed herein.…”

“…Thus, higher amounts of the mercury dithiolate species distinguishe P. idrijaensis equipped with the mer operon. The two Hg(SR) 3 references from our database (Manceau et al, 2019) were both unsuitable models.…”

Uranium speciation in weathered granitic waste rock piles: an XAFS investigation

“…It must be emphasized that the examination of the disordered U-complex can be performed using the highresolution (HR) XANES technique which can provide better geometric information due to its insensitivity to structural disorder and superior elemental sensitivity. 52 The technique has been utilized for the structural characterization of model U(VI) minerals with the combination of ab initio multiple scattering theory. However, it was noted that this technique is complimentary and must be coupled with ab initio quantum chemical calculations.…”