Smith C A, Baker H M, Baker E N
Department of Chemistry and Biochemistry, Massey University, Palmerston North, New Zealand.
J Mol Biol. 1991 May 20;219(2):155-9. doi: 10.1016/0022-2836(91)90557-m.
As part of a comparative study on the binding of different metals and anions by human lactoferrin, we have prepared and crystallized: (1) dicupric lactoferrin with Cu2+ and carbonate in each site (Cu2Lf); and (2) a lactoferrin complex with Cu2+ and carbonate in one site, and Cu2+ and oxalate in the other (Cu2oxLf). Crystals of Cu2Lf are orthorhombic: a = 155.9, b = 97.0, c = 56.0 A, space-group P2(1)2(1)2(1); those of Cu2oxLf are also orthorhombici a = 155.9, b = 97.1, c = 56.2 A, space-group P2(1)2(1)2(1). Both are isomorphous with diferric human lactoferrin, Fe2Lf. Diffractometer data to 2.6 A and 2.5 A have been collected for Cu2Lf and Cu2oxLf, respectively. Difference maps show that the main effect of substitution of Cu2+ for Fe3+ is a small shift (0.5 to 1.0 A) in the metal position in each site. For Cu2oxLf the oxalate ion is found to be accommodated in the C-lobe, bound to copper in a bidentate mode, causing only small local changes, in the positions of adjacent Arg and Tyr side-chains.
