113Cd NMR study of a metallothionein fragment. Evidence for a two-domain structure.
A 32-residue polypeptide fragment, designated alpha I, of rat liver metallothionein obtained by subtilisin digestion was studied by 113Cd NMR. The amino acid composition of the fragment corresponded to residues 30-61 of the metallothionein primary structure, and it contained 3.4 g atoms of Cd2+/mol of alpha I-fragment. Four 113Cd resonances were observed, three of which had identical chemical shifts to those assigned to the four-metal cluster in human liver metallothionein-2 under the same pH and buffer conditions. The 5-ppm chemical shift difference between the remaining resonance assigned to the four-metal cluster in the intact protein can be explained to result from the removal of the NH2-terminal polypeptide fragment containing the three-metal cluster. These results provide unambiguous evidence for the two-domain structure of metallothionein, containing a separate three- and a four-metal cluster.
D000818:Animals; D002104:Cadmium / Q000032:analysis; D006801:Humans; D008099:Liver / Q000032:analysis*; D009682:Magnetic Resonance Spectroscopy; D008667:Metalloproteins / Q000302:isolation & purification; D008668:Metallothionein / Q000302:isolation & purification; D010446:Peptide Fragments; D051381:Rats
D008667:Metalloproteins; D010446:Peptide Fragments; D002104:Cadmium; D008668:Metallothionein