Structural and functional studies of vertebrate metallothioneins: cross-talk between domains in the absence of physical contact

Molecular cloning, the characterization of metallothionein and catalase, and the evaluation of testicular toxicity of Cd in the Chinese fire-bellied newt (Cynops orientalis)

Cadmium (Cd) is an environmental toxicant and a nonessential metal. Cd can attack a wide range of organs, such as the liver, kidney, lung, ovary, testis, brain, and muscle in vertebrates. Among these organs, the testis might be the most sensitive organ to Cd toxicity. Metallothionein (MT) is a cysteine-rich protein with a low molecular weight, that can bind with Cd and eliminate reactive oxygen species (ROSs). Hydrogen peroxide, which as a crucial type of ROS that is induced by Cd, can be eliminated by catalase (CAT) in the self-protection of cells and to realize Cd toxicity resistance. To investigate the functions of MT and CAT in the testis of Cynops orientalis, we cloned the full-length MT and CAT genes of C. orientalis for the first time. Immunofluorescence results demonstrated that MT and CAT were expressed in Sertoli cells and all spermatogenic cells in the testis of C. orientalis. The results of the ultrastructural damage assay demonstrated that there were various impairments, which included organelle vacuolization, abnormal chromatin distribution, and apoptotic bodies, in somatic cells that were exposed to Cd. However, the anomalies of spermatozoa were located mainly in the mid-piece and head, many of which showed severely impaired structures. The results demonstrated that MT and CAT expression had distinct patterns in response to various Cd concentrations: an increase in MT mRNA levels with elevated Cd levels and a persistent increase in CAT mRNA levels with elevated Cd levels. These results suggested that MT and CAT play roles in Cd toxicity resistance in the testis and that the expression of CAT may be a better biomarker than the expression of MT for assessing Cd pollution.

Crosstalk of the structural and zinc buffering properties of mammalian metallothionein-2

Structural insights into partially Zn(ii)-depleted MT2 species and their zinc buffering properties are presented and discussed.

Metal Substitution and Solvomorphism in Alkylthiolate-Bridged Zn3 and HgZn2 Metal Clusters

The impact of substituting Hg(II) for Zn(II) in a thiolate-bridged trinuclear cluster with parallels to a metallothionein metal cluster was investigated. A new solvomorph of [Zn(ZnL)₂](ClO₄)₂ (1) (L = N-(2-pyridylmethyl)-N-(2-(ethylthiolato)-amine) and five solvomorphs of a new compound [Hg(ZnL)₂](ClO₄)₂ (2) were characterized by single-crystal X-ray crystallography. The interplay of hydrogen bonding and aromatic-packing interactions in producing lamellar, 2D lamellar, and columnar arrangements of complex cations in the crystalline state is discussed. Both variable temperature proton nuclear magnetic resonance and electrospray ion-mass spectrometry (ESI-MS) suggest that the complex ions of 1 and 2 are the predominant solution species at moderate concentrations. ESI-MS was also used to monitor differences in metal ion redistribution as 1 was titrated with Hg(ClO₄)₂ and [HgL(ClO₄)]. These studies document the facile replacement of Zn(II) by Hg(II) with the preservation of the overall structure in thiolate-rich clusters.

Sulfonamide inhibition studies of the γ-carbonic anhydrase from the Antarctic bacterium Colwellia psychrerythraea

The Antarctic bacterium Colwellia psychrerythraea encodes for a γ-class carbonic anhydrase (CA, EC 4.2.1.1), which was cloned, purified and characterized. The enzyme (CpsCAγ) has a moderate catalytic activity for the physiologic reaction of CO2 hydration to bicarbonate and protons, with a k(cat) 6.0×10(5) s(-1) and a k(cat)/K(m) of 4.7×10(6) M(-1) s(-1). A series of sulfonamides and a sulfamate were investigated as inhibitors of the new enzyme. The best inhibitor was metanilamide (K(I) of 83.5 nM) followed by indisulam, valdecoxib, celecoxib, sulthiame and hydrochlorothiazide (K(I)s ranging between 343 and 491 nM). Acetazolamide, methazolamide as well as other aromatic/heterocyclic derivatives showed inhibition constants between 502 and 7660 nM. The present study may shed some more light regarding the role that γ-CAs play in the life cycle of psychrophilic bacteria as the Antarctic one investigated here, by allowing the identification of inhibitors which may be useful as pharmacologic tools.

Hepatic metallothioneins in molecular responses to cobalt, zinc, and their nanoscale polymeric composites in frog Rana ridibunda

Despite numerous studies suggesting a dramatic decline of amphibians, the biochemical mechanisms of adaptation in these animals to polluted environment are poorly studied. The aim of this study was to elucidate the ability to release cobalt (Co) and zinc (Zn) from their nanoscale complexes (NCs) derived from the polymeric substance of N-vinylpyrrolidone (PS) in the liver of amphibian (Rana ridibunda). Frog males were subjected to 14days exposure to waterborne Co(2+) (50μg/L), Zn(2+) (100μg/L), as well as corresponding concentrations of Co-NC, Zn-NC or PS. Main attention was paid to MT's interrelations with indices of stress and toxicity. Only Co(2+) and Zn(2+) caused elevation of the correspondent metal in MTs. Co(2+) caused down-regulation of cathepsin D activity, while Zn(2+), Zn-NC and the PS up-regulated this activity. Zn(2+) provoked 1.6 times increase of metal-bounded form of the MT (MT-Me), while all other exposures caused the elevation of the ratio of MT total protein concentration (MT-SH) and concentrations of the MT-Me and/or immunoreactive (MTi) form (up to ~10 times) accompanied by a decrease in the levels of oxyradicals. The increased DNA fragmentation and down-regulation of caspase-3 activity in relation to the redox state of glutathione and/or lactate/pyruvate were shown at all exposures. These data indicate the vulnerability of the redox state of cellular thiols and inability to release Co and Zn from NCs in frog's liver.

Metallothionein biosynthesis as a detoxification mechanism in mercury exposure in fish, spotted scat (Scatophagus argus)

It is of crucial importance to study on the biomarkers types to assess the specification of the pollutants and health status of marine ecosystems in environmental evaluation projects. In this respect, total metallothionein biosynthesis and mercury bioaccumulation in the liver and gills under acute mercury exposure were investigated in fish, Scat (Scatophagus argus). Spotted scat was exposed to different mercury concentrations (0, 10, 20, 30) for 24, 48, 72 h. Total MT levels were determined by enzyme-linked immunosorbent assay (ELISA) method. Mercury contents were determined through cold vapor atomic absorption spectrometry (CVAAS). Induction of MT during exposure was tissue specific, displaying different response pattern in gills and liver. Mercury accumulated in liver much higher than in gills and the latter also showed lower MT level (P<0.05). MT biosynthesis in liver showed a significant (P<0.05) increase after exposure to different mercury concentration with increase in exposure time, whereas total MT content did not significantly (P>0.05) change in gills except for 72 h exposure at 30 μg l(-1). Nonetheless, the relationship between MT biosynthesis and Mercury bioaccumulation in both tissues was significant (P<0.05). The results suggest that this form of MT in S. argus was Hg inducible and could be extended as a biomarker of mercury pollution in marine ecosystems.

Arsenic metalation of seaweed Fucus vesiculosus metallothionein: the importance of the interdomain linker in metallothionein

The presence of metallothionein in seaweed Fucus vesiculosus has been suggested as the protecting agent against toxic metals in the contaminated waters it can grow in. We report the first kinetic pathway data for A3+ binding to an algal metallothionein, F. vesiculosus metallothionein (rfMT). The time and temperature dependence of the relative concentrations of apo-rfMT and the five As-containing species have been determined following mixing of As3+ and apo-rfMT using electrospray ionization mass spectrometry (ESI MS). Kinetic analysis of the detailed time-resolved mass spectral data for As3+ metalation allows the simulation of the metalation reactions showing the consumption of apo-rfMT, the formation and consumption of As1- to As4-rfMT, and subsequent, final formation of As5-rfMT. The kinetic model proposed here provides a stepwise analysis of the metalation reaction showing time-resolved occupancy of the Cys7 and the Cys9 domain. The rate constants (M(-1) s(-1)) calculated from the fits for the 7-cysteine gamma domain are k1gamma, 19.8, and k2gamma, 1.4, and for the 9-cysteine beta domain are k1beta, 16.3, k2beta, 9.1, and k3beta, 2.2. The activation energies and Arrhenius factors for each of the reaction steps are also reported. rfMT has a long 14 residue linker, which as we show from analysis of the ESI MS data, allows each of its two domains to bind As3+ independently of each other. The analysis provides for the first time an explanation of the differing metal-binding properties of two-domain MTs with linkers of varying lengths, suggesting further comparison between plant (with long linkers) and mammalian (with short linkers) metallothioneins will shed light on the role of the interdomain linker.