/sup 113/Cd NMR studies on metal-thiolate cluster formation in rabbit Cd(II)-metallothionein: evidence for a pH dependence
The formation of two metal-thiolate clusters in rabbit liver metallothionein 2 (MT) has been examined by /sup 113/Cd NMR spectroscopy at pH 7.2 and 8.6. The chemical shifts of the /sup 113/Cd resonances developing in the course of apoMT titration with /sup 113/Cd(II) ions have been compared with those of fully metal occupied /sup 113/Cd/sub 7/-MT. At pH 7.2 and at low metal occupancy (<4), a cooperative formation of the four-metal cluster (cluster A) occurs. Further addition of /sup 113/Cd(II) ions generates all the resonances of the three-metal cluster (cluster B) in succession, suggesting cooperative metal binding to this cluster also. In contrast, similar studies at pH 8.6, at low metal occupancy (<4), reveal a broad NMR signal centered at 688 ppm. This observation indicates that an entirely different protein structure exists. When exactly 4 equiv of /sup 113/Cd(II) are bound to apoMP, the /sup 113/Cd NMR spectrum changes to the characteristic spectrum of cluster A. Further addition of /sup 113/Cd(II) ions again leads to the cooperative formation of cluster B. These results stress the determining role of the cluster A domain on the overall protein fold. The observed pH dependence of the cluster formation in MT can be rationalized by the different degree of deprotonation of the cysteine residues (pK/sub a/ approx. 8.9), i.e., by the difference in the Gibbs free energy required to bind Cd(II) ions to the thiolate ligands at both pH values.
- Research Organization:
- Universitaet Zuerich (Switzerland)
- OSTI ID:
- 6463397
- Journal Information:
- Biochemistry; (United States), Journal Name: Biochemistry; (United States) Vol. 27:18; ISSN BICHA
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
62 RADIOLOGY AND NUCLEAR MEDICINE
AMINO ACIDS
ANIMALS
BETA DECAY RADIOISOTOPES
BETA-MINUS DECAY RADIOISOTOPES
CADMIUM 113
CADMIUM COMPOUNDS
CADMIUM ISOTOPES
CARBOXYLIC ACIDS
CATIONS
CHARGED PARTICLES
CHEMICAL REACTIONS
CHEMICAL SHIFT
CROSS-LINKING
CYSTEINE
EVEN-ODD NUCLEI
INTERMEDIATE MASS NUCLEI
IONS
ISOMERIC TRANSITION ISOTOPES
ISOTOPES
LIGANDS
MAGNETIC RESONANCE
MAMMALS
METALLOPROTEINS
METALLOTHIONEIN
NMR SPECTRA
NUCLEAR MAGNETIC RESONANCE
NUCLEI
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC SULFUR COMPOUNDS
PH VALUE
POLYMERIZATION
PROTEINS
RABBITS
RADIOISOTOPES
RESONANCE
SPECTRA
STABLE ISOTOPES
THIOLS
VERTEBRATES
YEARS LIVING RADIOISOTOPES