Residues 51-82

The gap correcting for the length variability in the CDR 2 region has been placed to be centered on position 63, resulting in an 8-residue gap in the VL domains (L59-L66, placed between L50 and L51 according to Kabat nomenclature) and a one- to four-residue gap in VH domains (between H52 and H53 according to Kabat).

In Va domains, a second gap has been placed in positions A74 and A75 to reflect the way in which the C-terminal branch of the CDR A2 loop is retracted from the dimer interface compared to the CDR 2 of other immunoglobulin variable domains. While in all other variable domains the descending branch of CDR 2 is part of the "inner" b-sheet (the one which forms the dimer interface), the descending branch of the Va CDR 2 (residues 67-73) is more closely associated with the "outer" b-sheet, although the hydrogen bonds to the strand formed by residues 78-82 are not very well conserved in the few Va -structures known. Again, like in the CDR 1, this splitting of the CDR 2 length variability into two insertion points necessitates more positions than allowed for in the IMGT nomenclature.