IRON SUPEROXIDE-DISMUTASE FROM THE ARCHAEON SULFOLOBUS-SOLFATARICUS -AVERAGE HYDROPHOBICITY AND AMINO-ACID WEIGHT ARE INVOLVED IN THE ADAPTATION OF PROTEINS TO EXTREME ENVIRONMENTS

The iron-superoxide dismutase in the thermoacidophilic archaeon Sulfol obus solfataricus has a homodimeric structure with a metal content of 0.7 atom of iron per subunit, The enzyme is insensitive to cyanide inh ibition, sensitive to inactivation by H2O2 and is the most heat resist ant SOD known so far being its half-life 2 h at 100 degrees C. Its pri mary structure was determined by a profitable combination of advanced mass spectrometry and automated sequence analysis of peptides obtained after cleavage of the purified protein. The enzyme subunit is compose d of 210 amino acid residues accounting for a relative molecular mass of 24 112. It does not contain cysteine residues and has a high averag e of both hydrophobicity and amino acid weight. Vice versa, the hydrop hobicity is lower in halophilic SODs. Therefore, it seems that the ave rage hydrophobicity is involved in the adaptation of proteins to extre me environments. The multiple alignment of the primary structure of ar chaeal and thermophilic eubacterial SODs indicated that archaeal SODs evolved separately from the thermophilic eubacterial SODs and that hal ophiles originated from a gene different from that of thermophilic arc haea. (C) 1997 Elsevier Science B.V.