Exploring peptide binding to the disease associated HLA-DQ2.5 molecule by the use of peptide libraries

We here describe that soluble HLA-DQ2 (sDQ2)molecules, when expressed in Drosophila melanogaster S2insect cells without a covalently tethered peptide, associatetightly with the D. melanogaster calcium binding proteinDCB-45. The interaction between the proteins is stable in S2cell culture and during affinity purification, which is done athigh salt concentrations and pH 11.5. After affinity purifica-tion, the sDQ2/DCB-45 complex exists in substantialquantities next to a small amount of free heterodimericsDQ2 and large amounts of aggregated sDQ2 free of DCB-45. Motivated by the stable complex formation and ourinterest in the development of reagents which inhibit HLA-DQ2 peptide binding, we have further characterized thesDQ2/DCB-45 interaction. Several lines of evidence indicatethat an N-terminal fragment of DCB-45 is involved in theinteraction with the peptide binding groove of sDQ2. Furthermapping of this fragment of 54 residues identified apentadecapeptide with high affinity for sDQ2 which mayserve as a lead compound for the design of HLA-DQ2blockers.