Biotinylation of class I MHC molecules abrogates recognition by W6/32 antibody

W6/32 is one of the most common monoclonal antibodies (mAb) used to characterize human class I major histocompatibility complex (MHC) molecules. It recognizes a conformational epitope on the intact MHC molecule containing both beta2-microglobulin (beta2-m) and the heavy chain. Labelling proteins by biotinylation is a very useful technique of for their detection, purification and analysis. A common method for biotinylating proteins is through the use of N-hydroxysuccinimide (NHS) biotin or Sulfo-NHS-biotin where the free amino groups on the protein are used for coupling the biotin moiety. However, W6/32 was unable to effectively immunoprecipitate biotinylated human class I MHC molecules including the human non-classical HLA-G molecule. FACScan analysis confirmed that biotinylating human class I MHC and HLA-G molecules prevents the recognition of these molecule by W6/32. In contrast, the recognition by another conformation-dependent monoclonal antibody, ME1, specific to HLA-B27 molecules, remained totally unaffected.