Expression, purification, crystallization and crystallographic characterization of dimeric and monomeric human neutrophil gelatinase associated lipocalin (NGAL)

Crystals of the monomeric and dimeric forms of human neutrophil gelatinase associated lipocalin have been grown in hanging-drop vapor-diffusion trials using PEG as a precipitating agent with recombinant protein expressed in a baculovirus-based system. Crystals of monomeric NGAL belong to the cubic space group P432 with lattice constants a = b = c = 126.6 Å; crystals of dimeric NGAL belong to the tetragonal space group P4₁2₁2 (or its enantiomorph P4₃2₁2) with lattice constants a = b = 54.14 and c = 121.56 Å. Isomorphous crystals of the NGAL dimer can be grown in the presence of ligand: the tripeptide N-formyl-Met-Leu-Phe.