Human versus mouse Beta 2 microglobulin alters TCR antigen recognition kinetics with mouse MHCI

There are three isoforms of Beta2 microglobulin (B2m) identified in mice and they differ by a single amino acid residue. To study how B2m can modify the peptide binding pocket of MHCI we turned to the comparison of mouse (mB2m) and human (hB2m). It is known that hB2m forms more stable with mouse MHCI heavy chain as compared to mb2m and hB2m is often the choice for most pMHCI tetramer production. Analysis of mB2m and hB2m tetramer (GP33 41M) following LCMV infection revealed no difference in percentage of tetramer positive cells but an increase was observed in staining intensity (MFI) of hB2m. Using steered molecular dynamics we found that there were allosteric effects with mB2m displaying more movement within the binding pocket than hB2m. Consistent with this we saw increased 2D affinity for antigen MHC D band K bhB2m complexes for OT1 and P14 TCRs, respectively. We also measured the force effects on bond lifetime between TCR and pMHC using biomembrane force probe (BFP) and DNA tension sensor. For OTI, we found that mB2m complexes had a longer bond lifetime measured by both methods. We observed signaling and functional effects consistent with the 2D affinity and bond lifetime measurements in mouse verses human B2m. For example, mB2m leads to increased levels of activated LCK (pY394/505) in OT1 T cells. Therefore, alterations in B2m effect the distal peptide binding domain of MHCI and suggests dynamic allostery may influence antigen recognition by TCR. 5T32NS115664-03 5R01AI147641-03