The three-dimensional structure of diferric buffalo lactoferrin has been de
termined at 3.3 Angstrom resolution. The structure was solved by molecular
replacement using the coordinates of diferric human lactoferrin as a search
model and was refined by simulated annealing (X-PLOR). The final model com
prises 5316 protein atoms for all 689 residues, two Fe3+ and two CO32- ions
. The final R factor was 21.8% for 11 711 reflections in the resolution ran
ge 17.0-3.3 Angstrom. The folding of buffalo lactoferrin is essentially sim
ilar to that of the other members of the transferrin family. The significan
t differences are found in the dimensions of the binding cleft and the inte
rlobe orientation. The interlobe interactions are predominantly hydrophobic
in nature, thus facilitating the sliding of two lobes owing to external fo
rces. The interdomain interactions are comparable in the N and C lobes.