Primary Citation of Related Structures: 1IRN, 1IRO
PubMed Abstract:
The Zn(Scys)4 unit is present in numerous proteins, where it assumes structural, regulatory, or catalytic roles. The same coordination is found naturally around iron in rubredoxins, several structures of which have been refined at resolutions of, or near to, 1 A ...
The Zn(Scys)4 unit is present in numerous proteins, where it assumes structural, regulatory, or catalytic roles. The same coordination is found naturally around iron in rubredoxins, several structures of which have been refined at resolutions of, or near to, 1 A. The fold of the small protein rubredoxin around its metal ion is an excellent model for many zinc finger proteins. Zn-substituted rubredoxin and its Fe-containing counterpart were both obtained as the products of the expression in Escherichia coli of the rubredoxin-encoding gene from Clostridium pasteurianum. The structures of both proteins have been refined with an anisotropic model at atomic resolution (1.1 A, R = 8.3% for Fe-rubredoxin, and 1.2 A, R = 9.6% for Zn-rubredoxin) and are very similar. The most significant differences are increased lengths of the M-S bonds in Zn-rubredoxin (average length, 2.345 A) as compared with Fe-rubredoxin (average length, 2.262 A). An increase of the CA-CB-SG-M dihedral angles involving Cys-6 and Cys-39, the first cysteines of each of the Cys-Xaa-Xaa-Cys metal binding motifs, has been observed. Another consequence of the replacement of iron by zinc is that the region around residues 36-46 undergoes larger displacements than the remainder of the polypeptide chain. Despite these changes, the main features of the FeS4 site, namely a local 2-fold symmetry and the characteristic network of N-H...S hydrogen bonds, are conserved in the ZnS4 site. The Zn-substituted rubredoxin provides the first precise structure of a Zn(Scys)4 unit in a protein. The nearly identical fold of rubredoxin around iron or zinc suggests that at least in some of the sites where the metal has mainly a structural role-e.g., zinc fingers-the choice of the relevant metal may be directed by its cellular availability and mobilization processes rather than by its chemical nature.
Related Citations:
Crystallographic Refinement of Rubredoxin at 1.2 Angstroms Resolution Watenpaugh, K.D., Sieker, L.C., Jensen, L.H. (1980) J Mol Biol 138: 615
Refinement of the Model of a Protein. Rubredoxin at 1.5 Angstroms Resolution Watenpaugh, K.D., Sieker, L.C., Herriott, J.R., Jensen, L.H. (1973) Acta Crystallogr B 29: 943
Structure of Rubredoxin. An X-Ray Study to 2.5 Angstroms Resolution Herriott, J.R., Sieker, L.C., Jensen, L.H., Lovenberg, W. (1970) J Mol Biol 50: 391
Organizational Affiliation:
European Molecular Biology Laboratory, Deutsches Elektronen Synchrotron, Hamburg, Germany.
Download Mendeley
