Data Collection from Very Thin HLA Crystals Using Synchrotron Radiation

Abstract

HLA molecules are polymorphic cell surface glycoproteins involved in the cellular immune response against viruses. Cytotoxic T-cells recognize viral peptides derived from intracellular processing that are complexed to HLA (Townsend et al., 1986; Maryanski et al., 1986). HLA class I molecules are heterodimers: the heavy chain has three domains (alpha1, alpha2, alpha3), and the light chain (beta2-microglobulin) consists of a single domain with homology to immunologlobulin constant regions. The heavy chain alphal and alpha2 domains are polymorphic between specificities, and the more constant alpha3 domain has homology to antibody constant domains and to the HLA light chain (reviewed in Hood et al., 1983). In order to understand how the polymorphic residues are distributed on the HLA structure, and how HLA interacts with peptides and T-cell receptors, we initiated a structure determination of HLA-A2, a human histocompatibility molecule. The structure of HLA-A2 and the implications for understanding how HLA molecules function have been previously described (Bjorkman et al., 1987a; Bjorkman,1987b). This report will concentrate only upon the data collection and processing of HLA films taken using synchrotron radiation as an X-ray source. Most of the HLA data were collected at a synchrotron facility in order to maximize the amount of diffraction data available from each crystal. Both HLA crystals and protein were in short supply, and HLA crystals are very thin (~20 microns).