Functional dissociation of CD8 alpha's Ig homologue and connecting peptide domains.
The contribution of the CD8 alpha.IgV homologue domain to class I MHC binding was evaluated using a series of chimeric human CD8 alpha:Fc polypeptides incorporating alternative CD8 alpha extracellular domain components. Using a nonisotopic cellfree physical binding assay, those Fc chimeras encompassing the CD8 alpha.IgV homologue domain only (dissociated from the 48-amino acid CD8 alpha connecting peptide) were shown to retain the capacity of the complete CD8 alpha extracellular domain to bind to a recombinant soluble class I MHC alpha 3 domain unit or to intact class I MHC. The specificity of the CD8 alpha:class I MHC alpha 3 domain interaction was verified by mAb and soluble polypeptide blocking experiments. Furthermore, co-precipitation of an Fc chimera incorporating only the CD8 alpha.IgV homologue domain and a recombinant soluble class I MHC alpha 3 domain unit was accomplished. In addition, a glycosylphosphatidylinositol (GPI)-modified variant of the CD8 alpha.IgV homologue domain was generated via chimerization with the GPI signal sequence from decay-accelerating factor. GPI anchorage for this truncated CD8 alpha polypeptide was verified, and its capacity to promote intercellular adhesion through class I MHC binding was shown in a cell:cell binding assay. The findings indicate that the CD8 alpha.IgV homologue domain acts as an independent structural unit when dissociated from the CD8 alpha connecting peptide, and in so doing retains class I MHC binding capacity. This further establishes the principle that Ig superfamily domains from receptor:counter-receptor pairs can interact with each other as isolated units, providing an experimental path for tailoring therapeutically useful IgSF protein derivatives.
Institute of Pathology, Case Western Reserve University, Cleveland, OH 44106, USA.
H J
HJ
Meyerson
J H
JH
Huang
J D
JD
Fayen
H M
HM
Tsao
R R
RR
Getty
N S
NS
Greenspan
M L
ML
Tykocinski
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001665:Binding Sites; D018958:CD55 Antigens / Q000235:genetics; D016827:CD8 Antigens / Q000737:chemistry*; D016466:CHO Cells; D002352:Carrier Proteins / Q000235:genetics; D006224:Cricetinae; D017261:Glycosylphosphatidylinositols / Q000737:chemistry; D015789:HLA-A2 Antigen / Q000235:genetics; D006801:Humans; D007135:Immunoglobulin Variable Region / Q000737:chemistry* / Q000235:genetics; D058619:Maltose-Binding Proteins; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000737:chemistry* / Q000235:genetics; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000235:genetics; D017386:Sequence Homology, Amino Acid; D014407:Tumor Cells, Cultured
D018958:CD55 Antigens; D016827:CD8 Antigens; D002352:Carrier Proteins; D017261:Glycosylphosphatidylinositols; D015789:HLA-A2 Antigen; D007135:Immunoglobulin Variable Region; D058619:Maltose-Binding Proteins; D010446:Peptide Fragments; D011993:Recombinant Fusion Proteins