INS and type 1 diabetes mellitus: This observation is consistent with a notion that the I-Ag7 T1D-susceptible MHC class II molecule, which has a positively charged patch in the surface area near the p9 pocket due to the lack of a negatively charged amino acid residue at the beta 57 position, engage TCRs having a negatively charged residue when p9 of peptides is not negatively charged (the position 20 of insulin B chain is glycine).