Recombinant superoxide dismutase from a hyperthermophilic archaeon, Pyrobaculum aerophilum

Superoxide dismutase (SOD) from the hyperthermophilic archaeon Pyrobaculum aerophilum (a facultative aerobe) has been cloned and expressed in a mesoph ilic host (Escherichia coli) as a soluble tetrameric apoprotein. The purifi ed apoprotein can be reconstituted with either Mn or Fe by heating the prot ein with the appropriate metal salt at an elevated temperature (95 degrees C). Both Mn- and Fe-reconstituted P. aerophilum SOD exhibit superoxide dism utase activity, with the Mn-containing enzyme having the higher activity. P . aerophilum SOD is extremely thermostable and the reconstitution with Mn(I I) can be performed in an autoclave (122 degrees C, 18 psi). The Mn(III) op tical absorption spectrum of Mn-reconstituted P. aerophilum SOD is distinct from that of most other MnSODs and is unchanged upon addition of NaN3. The optical absorption spectrum of Fe-reconstituted P. aerophilum SOD is typic al of Fe-substituted MnSODs and authentic Fe-SOD and exhibits a pH-dependen t transition with an effective pK(a) value higher than that found for Fe-su bstituted MnSOD from either E. coli or Thermus spp. Amino acid sequence ana lysis shows that the P. aerophilum SOD is closely related to SODs from othe r hyperthermophilic archaea (Aeropyrum pernix and Sulfolobus spp.), forming a family of enzymes distinct from the hyperthermophilic bacterial SOD from Aquifex pyrophilus and from mesophilic SODs.