The Paradigm That All Oxygen-Respiring Eukaryotes Have Cytosolic CuZn-Superoxide Dismutase and That Mn-Superoxide Dismutase Is Localized to the Mitochondria Does Not Apply to a Large Group of Marine Arthropods

Abstract

The enzyme superoxide dismutase (SOD), which catalyzes the dismutation of the superoxide radical, is present in the cytosol and mitochondria of all oxygen-respiring eukaryotes. The cytosolic form contains copper and zinc (CuZnSOD), whereas the mitochondrial form contains manganese (MnSOD). The latter protein is synthesized in the cytosol as a MnSOD precursor, containing an N-terminal mitochondrial-targeting sequence. CuZnSOD is sensitive toward cyanide (CN) and hydrogen peroxide (H2O2), but MnSOD is not. Assays for SOD activity in cytosol from the hepatopancreas of the blue crab, Callinectes sapidus, showed the presence of a CN/H2O2-insensitive form of SOD. No CN/H2O2-sensitive CuZnSOD was found. This unexpected phenomenon was shown to occur in all decapod crustacea (crabs, lobsters, shrimp) examined. The cytosolic and mitochondrial SODs of C. sapidus were purified by means of ion-exchange, size-exclusion, and reverse-phase HPLC. The cytosolic SOD is a homodimeric protein, which exists in a monomer-dimer equilibrium (24 kDa left and right arrow 48 kDa). The protein contains approximately 1 Mn per subunit. No copper or zinc is present. Amino acid sequence analysis identified the novel cytosolic SOD as a MnSOD precursor with an abnormal mitochondrial-targeting sequence. The mitochondrial SOD of C. sapidus is similar to the MnSOD found in other eukaryotes. N-Terminal amino sequences of mitochondrial and cytosolic blue crab MnSOD differ in several positions. The MnSODs are thus encoded for by two different genes. The paradigm that all eukaryotes contain intracellular CuZnSOD and that MnSOD occurs exclusively in the mitochondria appears not to apply to a large group of marine arthropods.

Purification, molecular cloning, and some properties of a manganese-containing superoxide dismutase from Japanese flounder (Paralichthys olivaceus)

“…The molecular mass of the tested Mn-SOD (70 kDa) is less than that expected for a tetrameric enzyme with 26 kDa subunits. Similar discrepancies between subunit molecular mass and the molecular mass of native Mn-SOD have been previously reported (Meier et al, 1994;Brouwer et al, 1997). In addition, all of these findings were consistent with previous reports that Mn-SOD was usually a homodimer or homotetramer (Abe and Okazaki, 1987;Streller et al, 1994;Brouwer et al, 1997;Blackman et al, 2005).…”

“…Although there were reports that some plants and bacteria had two or four Mn-SOD encoding genes (Miao et al, 1993;Zhu and Scandalios, 1993;Brouwer et al, 1997;Blackman et al, 2005), it was very interesting whether three active bands of Japanese flounder Mn-SOD in this study represented the expressed products from multiple gene compositions or not. We sequenced the independent clone containing the entire Japanese flounder Mn-SOD gene using its genomic DNA.…”

Models of Superoxide Dismutases

“…(One notable , exception is a large group of marine arthropods with no CuZnSOD that have a cytosolic MnSOD in its place (85).) Most CuZnSODs are homodimenc proteins, with each of the two equivalent subunits containing a copper and a zinc ion and a molecular weight of approximately 16,000.…”

Cu,Zn superoxide dismutase in Rhodotorula and Udeniomyces spp. isolated from sea water: cloning and sequencing the encoding region

“…It is reported that organisms that never abandoned the marine environment have no SODC. Instead, SODM (principally SODF on bacteria) is present (Brouwer et al, 1997(Brouwer et al, , 1998Arun and Subramania, 1998;Mourete and Diaz Salvago, 1999). Although different genera have been used in this study, to discuss the marine environment effect on the sod-1 gene, the terrestrial counterparts of the marine yeast species must be included.…”