THE AMINO-ACID-SEQUENCE OF RUSTICYANIN ISOLATED FROM THIOBACILLUS-FERROOXIDANS

The amino acid sequence of rusticyanin, a copper protein, purified from the iron-oxidizing bacterium Thiobacillus ferrooxidans was determined. Rusticyanin contained 154 amino acid residues in a single polypeptide chain and its molecular weight was calculated to be about 16400 based on the amino acid sequence. The N-terminal sequence up to the 20th residue of the protein apparently resembled those of Methylobacterium extorquens AM1 amicyanin and poplar leaf plastocyanin rather than those of azurin family proteins. In the C-terminal region of the sequence, rusticyanin had one cysteine, one histidine and one methionine which are conserved through many copper proteins. In the middle region of the sequence, rusticyanin was not similar to any other copper protein. The sequence nearby His84 of rusticyanin was similar to those of other copper proteins to some extent. However, Asn which follows His84 and is highly conserved in other copper proteins did not exist in rusticyanin. Therefore, it seemed difficult to conclude on the basis of the results obtained in the present study that His84 in rusticyanin was the fourth ligand to the copper atom.