Title : Structure of copper- and oxalate-substituted human
lactoferrin at 2.0 A resolution
Abstract :
- The three-dimensional structure of human dicupric monooxalate lactoferrin , Cu(2)oxLf, has been determined to 2.0 A resolution, using X-ray diffraction data collected by diffractometry to 2.5 A resolution, and oscillation photography on a synchrotron source to 2.0 A resolution
- Difference electron-density maps calculated between Cu(2)oxLf and both dicupric lactoferrin , Cu(2)Lf, and diferric lactoferrin , Fe(2)Lf, showed that the oxalate had replaced a carbonate in the C-terminal binding site , and that, relative to Cu(2)Lf, there were no significant differences in the N-terminal site
- The structure was then refined crystallographically by restrained least-squares methods
- The final model, in which the r.m.s. deviation in bond distances is 0.017 A, contains 5314 protein atoms (691 residues ), two Cu(2+) ions, one bicarbonate ion, one oxalate ion, 325 solvent molecules and one sugar residue
- The crystallographic R factor of 0.193 is for 46 134 reflections in the range 8.0 to 2.0 A resolution
- The oxalate ion is coordinated to copper in a 1,2-bidentate fashion, and the added bulk of the anion results in the rearrangement of the side chains of nearby arginine and tyrosine residues
- No other major alterations in the molecule can be observed, the overall protein structure being the same as that for Cu(2)Lf and Fe(2)Lf