Expression, refolding, crystallization and preliminary crystallographic study of MHC H-2Kk complexed with octapeptides and nonapeptides.

Major histocompatibility complex (MHC) molecules are heterodimeric cell-surface receptors that play a crucial role in the cellular immune response by presenting epitope peptides to T-cell antigen receptors (TCR). Although the structural basis of the peptide-MHC binding mechanism is becoming better understood, it is still difficult to predict a binding mode for an MHC of unknown structure. Therefore, as the first stage of a TCR-MHC interaction study, the crystal structures of the mouse H-2K(k) molecule in complex with both an octapeptide from Influenza A virus and a nonapeptide from simian virus SV40 were solved. Here, the expression, refolding, purification and crystallization of the two complexes are reported. For the H-2K(k)-HA(259-266) complex, crystals were obtained via an extensive screen using a nanodrop-dispensing robot and diffracted to 2.5 A resolution. For the H-2K(k)-SV40(560-568) complex, microscopic needles were initially obtained and their size was improved by macroseeding and a stepwise increase in precipitant concentration. Diffraction data to a resolution of 3.0 A were collected at a synchrotron facility.