Nickel superoxide dismutase

Nid has square planar coordination involving two bridging cysteine thiolates and two main chain N atoms (Fig. 4A). A similar structure has been described recently for the active site of nickel superoxide dismutase (NiSOD) [117,118] (Fig. 4B). In NiSOD, Ni(II) reacts with superoxide and is oxidized to Ni(III)-peroxide. On the other hand, ACS functions in reducing environments and Nij is thought to remain as Ni(II) throughout catalysis. Model chemistry supports this proposal indicating that Nip is much more... 

In contrast to the abundance of Fe-proteins, there are only six known nickel-containing enzymes hydrogenase, CO dehydrogenase (CODA), acetyl-CoA synthase (ACS), superoxide dismutase, urease, and S-methyl-CoM methylreductase. Among these enzymes, it exists in very diverse environments, including a dinickel site (urease), a Ni-Fe heterobinuclear site (hydrogenase), a Ni-Fe4S4 heterometallic... 

Superoxide dismutases may contain a range of metals Mn, Fe, or both Cu and Zn, and representatives of all these are found in prokaryotes. The nickel enzyme is noted later. 

Wuerges J, J-W Lee, Y-I Yim, H-S Yrm, S-O Kang, KD Carugo (2004) Crystal structure of nickel-containing superoxide dismutase reveals another type of active site. Proc Natl Acad Sci USA 101 8569-8574. 

Nickel is found in thiolate/sulflde environment in the [NiFe]-hydrogenases and in CODH/ACS.33 In addition, either a mononuclear Ni-thiolate site or a dinuclear cysteine-S bridged structure are assumed plausible for the new class of Ni-containing superoxide dismutases, NiSOD (A).34 [NiFe]-hydrogenase catalyzes the two-electron redox chemistry of dihydrogen. Several crystal structures of [NiFe]-hydrogenases have demonstrated that the active site of the enzyme consists of a heterodinuclear Ni—Fe unit bound to thiolate sulfurs of cysteine residues with a Ni—Fe distance below 3 A (4) 35-39 This heterodinuclear active site has been the target of extensive model studies, which are summarized in Section 6.3.4.12.5. 

Fig. 6.2. Schematic structure of the active site of copper-zinc superoxide dismutase [72]. The zinc ion can be substituted, among others, by copper(II), cobalt(II) and nickel(II) ions.

The above system is similar to that built into the protein superoxide dismutase (Fig. 6.2). The zinc can be replaced by several metal ions. Cobalt(II) and nickel(II) are pertinent here. The cobalt-copper system has J 17 cm-1 with S = 1 ground state [25]. The electronic relaxation times for the two ions are expected to be either equal or similar. The H NMR spectrum is shown in Fig. 6.8A. The assignment has been performed through several steps. 

A newly discovered nickel enzyme is superoxide dismutase (SOD) from the acti-nomycete Streptomyces sp [164,165]. In its protein properties, this enzyme is... 

Superoxide dismutases are found widely in nature where a variety of redox metals (copper, nickel, iron, and manganese) are used to catalyze the disproportionation reaction 202 + 2H+ > 02 I H202.66 The copper/zinc and manganese-... 

Superoxide dismutase (SOD) catalyzes the disproportionation of superoxide to peroxide and oxygen according to equation (2). Four different types of SOD are known, containing either Cu and Zn see Copper Proteins with Type 2 Sites), Fe, Mn, or Ni see Nickel Enzymes Cofactors). The Fe and Mn containing SODs have very similar structures and can be further subdivided into metal-specific (i.e. functioning only when the correct metal is bound) and cambialistic (functioning with either Fe or Mn bound to the active site). 

The nickel enzymes covered in this article can be divided into two groups redox enzymes and hydrolases. The five Ni redox enzymes are hydrogenase, CO dehydrogenase (CODH), acetyl-CoA synthase (ACS), methyl-Coenzyme M reductase (MCR), and superoxide dismutase (SOD). Glyoxalase-I and urease are Ni hydrolases. Ni proteins that are not enzymes are not covered, because they have been recently reviewed. These include regulatory proteins (NikR) and chaperonins and metal uptake proteins (CooJ, CooE, UreE, and ABC transporters). A recent crystal structure of NikR, shown in Figure l(i), is a notable recent achievement in this area. ... 

Choudhury BS, Lee J-W, Davidson G, Yim Y-I, Bose K, Sharma ML, Kang S-O, Cabelli DE, Maroney MJ. (1999) Examination of the nickel site structure in Streptomyces seoulensis superoxide dismutase reveals a sulfur-rich coordination environment. Riochem 38 3744-3752. 

Superoxide dismutase, more commonly called SOD, is an unusual enzyme that breaks down even the most destructive free radicals in the body. At least four different types of it are now known, involving five different trace elements as parts of the molecular structure. Those metals are iron, manganese, nickel, and, in one form of the enzyme, a combination of copper and zinc. Others may be discovered in the future. The SOD enzyme especially protects the nucleic acids of cells from attack by free radicals. This is very important because DNA damage is one way that cancer can develop in the body. 

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