Purification, crystallization and X-ray diffraction analysis of the extracellular part of the human Fc receptor for IgA, FcalphaRI (CD89).

FcalphaRI is the predominant receptor for IgA in the serum. Nevertheless, the interaction between the molecules that finally leads to an immune response is poorly understood. To investigate the structural requirements for IgA binding, the extracellular region of FcalphaRI was cloned and overexpressed in Escherichia coli. The resulting inclusion-body protein was refolded and purified. Despite its deglycosylated state, this recombinant FcalphaRI retained its ability to bind human IgA. The protein crystallized spontaneously as microcrystalline needles. Recrystallization yielded crystals belonging to a primitive monoclinic space group. A complete 2.8 A resolution X-ray diffraction data set was collected using synchrotron radiation.