Primary structure of the variable regions of two canine immunoglobulin heavy chains

Abstract

The complete amino acid sequences of the variable regions of two canine immunoglobulin H chains (VH) were determined by automated Edman degradation and were strongly homologous to the human VHIII subgroup. The canine sequences were identical with each other at 76 of 113 residue positions. Twenty-three of the 37 differences are located within the 4 hypervariable regions previously defined by the sequences of several human VHIII proteins. Forty-five of 77 framework residue positions are invariant in the 7 human and 2 canine VHIII proteins which were completely sequenced. The canine proteins are 78% homologous to the framework of the human prototype. Phylogenetically associated residues before the 1st hypervariable region were confirmed and several potential phylogenetically associated residues were identified between the 1st and 3rd hypervariable regions. This study represents the 1st complete amino acid sequences of VH regions of spontaneously occurring, nonhuman homogeneous immunoglobulins. The data demonstrate a high degree of preservation of VHIII structure in another species.