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United States Department of Agriculture

Agricultural Research Service

Title: Functional Analysis of Polymorphic Residues Reveals Fine Structural Differences Between Avian (Bfiv) and Human (Hla-A2) Class I Glycoproteins

Authors
item Fulton, Janet
item Thacker Eileen L, - IOWA STATE UNIV AMES IA
item Bacon, Larry
item Hunt, Henry

Submitted to: European Journal of Immunology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 8, 1995
Publication Date: N/A

Interpretive Summary: A chicken gene that produces a protein important for viral disease resistance was obtained and its DNA sequence was determined. Alterations were made in this gene that affected the protein's structure. One of these structural changes altered the protein so that it could no longer function for viral resistance. The other structural change allowed normal viral resistance to occur but affected the shape of the protein on the surface of cells. These studies aid in understanding how genes determining cell surface proteins can affect interactions between cells and confer viral disease resistance.

Technical Abstract: Similarities between the physical structures of avian and mammalian MHC class I glycoproteins have been proposed by comparative alignment of their amino acid sequences. To investigate the physical structure of the chicken class I glycoprotein we have cloned the cDNA representing the BFIV locus of the B21 haplotype. A unique, chimeric class I glycoprotein was constructed by incorporating an epitope tag (FLAG) at the N terminus. Monoclonal antibodies to the FLAG epitope served to monitor cell surface expression for functional analysis of the BFIV21 class I glycoprotein. The chimeric class I glycoprotein was expressed in target cells using an ALV derived retrovirus vector (RCASBP). Functional analysis employing site directed mutagenesis identified BF amino acid residues forming serologic epitopes as well as residues important in antigen presentation to ALV induced cytotoxic T lymphocytes. BF residues 78 and 81 (HLA 79 and 82) form an antibody epitope with a slight effect on ALV antigen presentation, consistent with their predicted orientation based on the HLA-A2 crystal structure. Alignment of the BFIV21 sequence with previously published BFIV sequences revealed polymorphisms at position 34 (HLA34), a monomorphic residue in HLA and H-2. Residue 34 is located in pocket B and contacts the main chain carbon of bound peptides in HLA-A2. Studies with HLA-A2 have shown that changes in residue 34 do not affect viral peptide presentation. In contrast, a site directed substitution in residue 34 dramatically alters ALV antigen presentation by the BFIV21 class I glycoprotein. These data indicate that the fine physical structure of chicken class I is similar to HLA along the alpha 1 alpha helix, whereas the side chain orientation of internal residues impacting pocket B are altered.

Last Modified: 11/24/2014
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