title: Cd-metallothionein-a test object for dark-field studies of protein structure.
abstract: Cadmium-metallothionein contains about six metal atoms per 6,000 molecular weight, reflecting the high proportion of cystein residues in the structure. Because of the strong scattering from probable Cd-S (Cyst)3 complexes, the protein is unambiguously visualized by conventional tilted beam dark-field electronmicroscopy. The projections of the structure correspond to free, aggregated and partially denatured forms of the presumed native structure, a hexahedral mass, 36 multiplied by 25 multiplied by 16 A. Relaxed states of this structure show that the molecule is comprised of two similar, covalently linked "half-metallothineins", each comprised of three domains. Each of the six domains of the native structure is evidently formed by stacking of two characteristic scattering centers together, at a separation of 9 A. A speculative scheme for the folding of the native structure is presented. The results are interpreted as substantiating the fidelity of dark-field images of small proteins, and the cadmium-metallothionein molecule is suggested as a standard test object for the method.
mesh_terms: D000818:Animals; D002104:Cadmium; D008099:Liver / Q000032:analysis; D008297:Male; D008667:Metalloproteins; D008668:Metallothionein; D008854:Microscopy, Electron / Q000379:methods*; D008961:Models, Structural; D011489:Protein Denaturation; D051381:Rats; D012542:Scattering, Radiation
chemical_list: D008667:Metalloproteins; D002104:Cadmium; D008668:Metallothionein