Primary structure of molluscan metallothioneins deduced from PCR-amplified cDNA and mass spectrometry of purified proteins

• Published in: Biochimica et biophysica acta Vol. 1074; no. 3; pp. 371 - 377
• Main Authors: Unger, Michael E., Chen, Thomas T., Murphy, Constance M., Vestling, Martha M., Fenselau, Catherine, Roesijadi, G.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 06.08.1991; Elsevier
• Subjects: Amino Acid Sequence; Analytical, structural and metabolic biochemistry; Animals; Base Sequence; Biological and medical sciences; Blotting, Southern; Cadmium; cDNA; DNA; Fundamental and applied biological sciences. Psychology; Mass Spectrometry; Metalloproteins; Metallothionein; Metallothionein - chemistry; Metallothionein - isolation & purification; Molecular Sequence Data; Mollusc; N-Acetylation; Ostreidae - enzymology; Other metalloproteins; Oyster; PCR; Peptide Mapping; Polymerase Chain Reaction; Proteins; Sequence Alignment; Sequence Homology, Nucleic Acid; Tandem mass spectrometry; Trypsin; Polymerase chain reaction; Tandem mass spectrometry; Cadmium; N-Acetylation; Oyster; MT; cDNA; CvNAcMT and CvMT; Mollusc; Metallothionein; PCR; bp; Metalloproteins; Molecular evolution; Complementary DNA; Bivalvia; Crassostrea virginica; Peptide fragment; Mass spectrometry MS/MS; Invertebrata; Mollusca; Molecular cloning; Comparative study; Aminoacid sequence
• DOI: 10.1016/0304-4165(91)90087-W
• ISSN: 0304-4165; 0006-3002

The primary structure of metallothioneins (MT) of a mollusc, the oyster Crassostrea virginica, was determined by molecular cloning and mass spectrometry of purified proteins. The cloning strategy included PCR amplification of the responsible cDNAs from total cDNA using completely degenerate oligonucleotides (derived from the N-terminal amino acid sequence) and oligo(dT) 20 as primers. Primer extension off mRNA was used as an independent determination of the nucleotide sequence represented by the degenerate PCR primers. The deduced amino acid sequence was consistent with characteristics of class I MT. Twenty-one cysteine residues, were arranged in nine Cys-X-Cys motifs, five as Cys-Lys-Cys. A single Cys-X-X-Cys motif was also observed. Two MTs that differ only in the presence or absence of an N-acetyl group exist in this organism. Masses of tryptic peptides of purified MTs corresponded with those of peptides predicted from tryptic cleavages of the deduced amino acid sequence. Allowing for known N-terminal modifications, 96% of the deduced sequence was confirmed by mass spectrometry. Comparison (FASTA algorithm) of the primary structure of the oyster MTs with those of other species indicated a higher similarity with vertebrate MTs than with those of other invertebrates.