Crystallization and structure determination of goat lactoferrin at 4.0 Å resolution: A new form of packing in lactoferrins with a high solvent content in crystals

Abstract

Lactoferrin was purified from fresh samples of goat colostrums, saturated with Fe 3+ and CO 3 2- ions and crystallized by microdialysis method. The crystals belong to orthorhombic space group P2 12 12 1 with a=104.6 Å, b=153.8 Å, c=155.1 Å and Z=4. The quality of crystals was poor, thus the intensity data were restricted to 4.0 Å resolution only. The structure was determined by molecular replacement method using diferric buffalo lactoferrin as a model. The solution clearly indicated the presence of one molecule in the asymmetric unit, which corresponds to a Vm value of 7.1 Å 3/Da. The structure was refined with stringent constraints to an R-factor of 0.246 using all the reflections 15,870 to 4.0 Å resolution. The overall structure of goat lactoferrin is essentially similar to those of buffalo and bovine lactoferrins. However, the iron-binding environment in goat lactoferrin is somewhat different, in which 2 CO 3 2- ions have low occupancies. The solvent content of approximately 84% was very high in the present case which explains the fragility of the crystals of goat lactoferrin. In a way, it is very surprising that the crystals grow at all, although crystals with solvent as high as 89% have been reported.