The receptor with high affinity for IgE (Fc(epsilon)RI) is a tetrameric complex of an IgE binding alpha chain, a beta chain and a dimer of gamma chains. In the past we have found that the extracellular region of the alpha chain is solely responsible for ligand binding. In order to further characterize the receptor binding site, we use CHO cells to generate various transfectants secreting the extracellular domain of alpha with the hope of generating crystals for crystallographic analysis. The secreted alpha is active but the heterogenous glycosylation prevents crystallization. Deglycosylation by mutation of the seven N-linked glycosylation sites results in misfolding of the alpha chain in the endoplasmic reticulum of eukaryotic cells. For this reason, we have produced deglycosylated alpha chain in E-Coli. However, the deglycosylated alpha tends to aggregate and therefore is unsuitable for crystallization. Recently, by using limited deglycosylation, we have been able to produce a preparation of alpha chain which is crystallizing. The crystals difract at 4.5 angstrom and are therefore not good enough for standard crystallographic analysis. However, we hope that by adapting the conditions we will be able to produce better crystals.
