Sequence Determination and Molecular Characterization of Gigantin, a Cytotoxic Protein Produced by the MouldAspergillus giganteusIFO 5818

Gigantin is a 17-kDa ribonuclease secreted byAspergillus giganteusIFO 5818. The sequence of the genomic DNA coding for this protein is reported. The deduced amino acid sequence reveals nine amino acid variations with respect to α-sarcin, a well-characterized ribosome-inactivating protein fromA.giganteusMDH 18894. The peptides obtained after tryptic digestion of reduced and carboxyamidomethylated gigantin have been chromatographically separated. The analysis of these peptides in comparison to those originating from α-sarcin corroborates the above sequence differences. These do not sensibly modify the conformation of the protein, based on the coincidence of the circular dichroism and fluorescence emission spectra of the two proteins. The obtained results are discussed in terms of the involvement of the distinctive residues in the immunological and catalytic properties that distinguish gigantin from α-sarcin.