TY - JOUR

T1 - An Extremely Stable Interprotein Tetrahedral Hg(Cys)4 Core Forms in the Zinc Hook Domain of Rad50 Protein at Physiological pH

AU - Luczkowski, Marek

AU - Padjasek, Michal

AU - Tran, Jozef Ba

AU - Hemmingsen, Lars

AU - Kerber, Olga

AU - Habjanic, Jelena

AU - Freisinger, Eva

AU - Krezel, Artur

PY - 2022

Y1 - 2022

N2 - In nature, thiolate-based systems are the primary targets of divalent mercury (Hg-II) toxicity. The formation of Hg(Cys)(x) cores in catalytic and structural protein centers mediates mercury's toxic effects and ultimately leads to cellular damage. Multiple studies have revealed distinct Hg-II-thiolate coordination preferences, among which linear Hg-II complexes are the most commonly observed in solution at physiological pH. Trigonal or tetrahedral geometries are formed at basic pH or in tight intraprotein Cys-rich metal sites. So far, no interprotein tetrahedral Hg-II complex formed at neutral pH has been reported. Rad50 protein is a part of the multiprotein MRN complex, a major player in DNA damage-repair processes. Its central region consists of a conserved CXXC motif that enables dimerization of two Rad50 molecules by coordinating Zn-II. Dimerized motifs form a unique interprotein zinc hook domain (Hk) that is critical for the biological activity of the MRN. Using a series of length-differentiated peptide models of the Pyrococcus furiosus zinc hook domain, we investigated its interaction with Hg-II. Using UV-Vis, CD, PAC, and Hg-199 NMR spectroscopies as well as anisotropy decay, we discovered that all Rad50 fragments preferentially form homodimeric Hg(Hk)(2) species with a distorted tetrahedral HgS4 coordination environment at physiological pH; this is the first example of an interprotein mercury site displaying tetrahedral geometry in solution. At higher Hg-II content, monomeric HgHk complexes with linear geometry are formed. The Hg(Cys)(4) core of Rad50 is extremely stable and does not compete with cyanides, NAC, or DTT. Applying ITC, we found that the stability constant of the Rad50 Hg(Hk)(2) complex is approximately three orders of magnitude higher than those of the strongest Hg-II complexes known to date.

AB - In nature, thiolate-based systems are the primary targets of divalent mercury (Hg-II) toxicity. The formation of Hg(Cys)(x) cores in catalytic and structural protein centers mediates mercury's toxic effects and ultimately leads to cellular damage. Multiple studies have revealed distinct Hg-II-thiolate coordination preferences, among which linear Hg-II complexes are the most commonly observed in solution at physiological pH. Trigonal or tetrahedral geometries are formed at basic pH or in tight intraprotein Cys-rich metal sites. So far, no interprotein tetrahedral Hg-II complex formed at neutral pH has been reported. Rad50 protein is a part of the multiprotein MRN complex, a major player in DNA damage-repair processes. Its central region consists of a conserved CXXC motif that enables dimerization of two Rad50 molecules by coordinating Zn-II. Dimerized motifs form a unique interprotein zinc hook domain (Hk) that is critical for the biological activity of the MRN. Using a series of length-differentiated peptide models of the Pyrococcus furiosus zinc hook domain, we investigated its interaction with Hg-II. Using UV-Vis, CD, PAC, and Hg-199 NMR spectroscopies as well as anisotropy decay, we discovered that all Rad50 fragments preferentially form homodimeric Hg(Hk)(2) species with a distorted tetrahedral HgS4 coordination environment at physiological pH; this is the first example of an interprotein mercury site displaying tetrahedral geometry in solution. At higher Hg-II content, monomeric HgHk complexes with linear geometry are formed. The Hg(Cys)(4) core of Rad50 is extremely stable and does not compete with cyanides, NAC, or DTT. Applying ITC, we found that the stability constant of the Rad50 Hg(Hk)(2) complex is approximately three orders of magnitude higher than those of the strongest Hg-II complexes known to date.

KW - affinity

KW - Cys-rich protein

KW - mercury toxicity

KW - metal-sulfur cluster

KW - stability constant

KW - METAL-BINDING PROPERTIES

KW - STRAND BREAK REPAIR

KW - MERCURIC-CHLORIDE

KW - HG-199 NMR

KW - MRE11-RAD50-NBS1 COMPLEX

KW - MERCURY(II) COMPLEXES

KW - FORMATION-CONSTANTS

KW - DNA-REPLICATION

KW - COORDINATION

KW - STABILITY

U2 - 10.1002/chem.202202738

DO - 10.1002/chem.202202738

M3 - Journal article

C2 - 36222310

VL - 28

JO - Chemistry: A European Journal

JF - Chemistry: A European Journal

SN - 0947-6539

IS - 66

M1 - e202202738

ER -