Thiolates metallothioneins

Gold(I) thiolates also undergo reactions with disulfides. An example is 2,2-dithio-bis(2-nitrobenzoic acid) (ESSE) used as a kinetic probe of sulfhydryl reactivity in metallothioneins [39-42]. ESSE is readily attacked by metal-bound thiolates. The reaction with the open chain form of AuSTm seems to occur in two stages. The first attack involves the terminal sulfides and the second attack involves the bridging thiolates [19] ... 

Robbins, A.H. and Stout, C.D. (1992) Metallothioneins Synthesis, Structure and Properhes of Metallothioneins, Phytochelatins, and Metal-Thiolate Complexes (eds M.l. ShDman, C.F. Shawlll and KT. Suzuki), VCH Publishers, Weinheim, pp. 31—54. 

Silver(I) trifluoromethanethiolate (AgSCF3) has been used to prepare trifluoromethyl aryl sulfides by reaction with iodide.996 A mixed silver-zinc thiolate complex [Ag4Zn2(SC6H2-Pr -2,4,6)6(OTf)2] has been prepared by reaction of AgOTf with Zn[N(TMS)2]2 in the presence of the thiol.99 Solid-state 109Ag NMR can be a sensitive environment probe for silver thiolates,998 overall for biological thiolates ligands as cysteine,999 or proteins such as metallothionein.1000,1001... 

In mammals, as in yeast, several different metallothionein isoforms are known, each with a particular tissue distribution (Vasak and Hasler, 2000). Their synthesis is regulated at the level of transcription not only by copper (as well as the other divalent metal ions cadmium, mercury and zinc) but also by hormones, notably steroid hormones, that affect cellular differentiation. Intracellular copper accumulates in metallothionein in copper overload diseases, such as Wilson s disease, forming two distinct molecular forms one with 12 Cu(I) equivalents bound, in which all 20 thiolate ligands of the protein participate in metal binding the other with eight Cu(I)/ metallothionein a molecules, with between 12-14 cysteines involved in Cu(I) coordination (Pountney et ah, 1994). Although the role of specific metallothionein isoforms in zinc homeostasis and apoptosis is established, its primary function in copper metabolism remains enigmatic (Vasak and Hasler, 2000). 

Metallothioneins (MT) are unique 7-kDa proteins containing 20 cysteine molecules bounded to seven zinc atoms, which form two clusters with bridging or terminal cysteine thiolates. A main function of MT is to serve as a source for the distribution of zinc in cells, and this function is connected with the MT redox activity, which is responsible for the regulation of binding and release of zinc. It has been shown that the release of zinc is stimulated by MT oxidation in the reaction with glutathione disulfide or other biological disulfides [334]. MT redox properties led to a suggestion that MT may possesses antioxidant activity. The mechanism of MT antioxidant activity is of a special interest in connection with the possible antioxidant effects of zinc. (Zinc can be substituted in MT by some other metals such as copper or cadmium, but Ca MT and Cu MT exhibit manly prooxidant activity.)... 

Fig. 39. The three-metal-thiolate cluster in the j8-domain of rat liver metallothionein II (C. D. Stout, personal communication).

Weser, U., Hartmann, H. J. Copper thiolate proteins (metallothionein), Copper proteins and copper enzymes, Vol. 3, p. 151, Boca Raton, CRC press 1984... 

Since aromatic amino acids and cysteine are absent, there is no protein absorption above 270 nm. Metallothioneins exhibit a broad absorption peak, with the maximum at 190 mn. Absorptions due to the metal-thiolate complexes show as shoulders at 250 nm (Cd), 220 nm (Zn) and 270 nm (Cu).1458,1459 Theoretical predictions based on the amino acid sequence of the peptide chain indicate that the or-helical conformation is forbidden, and /3-structure is almost impossible to attain. CD and NMR studies on both the metal-containing and metal-free protein confirmed the predictions.1459 1460 However, metallothioneins are stable to tryptic digestion and the slow exchange of many peptide hydrogens of metallothionein with those of the solvent suggest that the protein has a compact and well-defined tertiary structure. 

The amino acid sequences of many mammalian metallothioneins are known.1152 They all contain 61 residues with the cysteine residues distributed along the full length of the polypeptide chain, and with N-acetylmethionlne and alanine at the N- and C-termini, respectively. All 20 cysteine residues are involved in the binding of up to seven metal ions via thiolate linkages. A typical amino acid sequence is shown in Figure 44. 

Several studies on models have been reported, both on the binding of a range of metals to apometallothionein and the design of ligands, particularly with Cys-X-Cys and Cys-X-Y-Cys arrangements as found for metallothionein.1163,1164 All metal derivatives appear to bind in metal-thiolate clusters.1149 Platinum has also been found bound to metallothionein in rat tissues following treatment with cisplatin and the trans isomer.1165... 

The protein metallothionein (MT) has a MW of 6000 and is rich in thiolate groups. It binds up to seven zinc(II), cadmium(II) and cobalt(II) ions. The seven ions are organized in two clusters. The so-called M4S11 cluster is shown in... 

Stillman MJ, Shaw CF III, Suzuki KT (1992) Metallothioneins. Synthesis, structure, and properties of metallothioneins, phytochelatins and metal-thiolate complexes. VCH Publishers, New York Stratford IJ, Hoe S, Adams GE, Hardy C, Williamson C (1983) Abnormal radiosensitizing and cytotoxic properties of ortho-substituted nitroimidazoles. Int J Radiat Biol 43 31-43 Stubbe J, Kozarich JW (1987) Mechanisms of bleomycin-induced DNA degradation. Chem Rev 87 1107-1136... 

As the focus of this review is on copper-dioxygen chemistry, we shall briefly summarize major aspects of the active site chemistry of those proteins involved in 02 processing. The active site structure and chemistry of hemocyanin (He, 02 carrier) and tyrosinase (Tyr, monooxygenase) will be emphasized, since the chemical studies described herein are most relevant to their function. The major classes of these proteins and their origins, primary functions, and leading references are provided in Table 1. Other classes of copper proteins not included here are blue electron carriers [13], copper-thiolate proteins (metallothioneines) [17], and NO reductases (e.g., nitrite [NIR] [18] or nitrous oxide [19]). 

While the mechanism of the interaction of these carboxylate complexes with the biological molecules that leads to their activity is not well understood, there is some evidence that the molecules can bind to N-donor and S-donor molecules in proteins. Bismuth(III) has been shown to bind most strongly to the thiolates in glutathione. There is some evidence that Bi(III) can replace metals such as Fe(III) in lactoferrin and transferrin or Zn(II) in metallothionein. ... 

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