title: Chicken T-cell receptor beta-chain diversity: an evolutionarily conserved D beta-encoded glycine turn within the hypervariable CDR3 domain.
abstract: Unlike mammals, chickens generate an immunoglobulin (Ig) repertoire by a developmentally regulated process of intrachromosomal gene conversion, which results in nucleotide substitutions throughout the variable regions of the Ig heavy- and light-chain genes. In contrast to chicken Ig genes, we show in this report that diversity of the rearranged chicken T-cell receptor (TCR) beta-chain gene is generated by junctional heterogeneity, as observed in rearranged mammalian TCR genes. This junctional diversity increases during chicken development as a result of an increasing base-pair addition at the V beta-D beta and D beta-J beta joints (where V, D, and J are the variable, diversity, and joining gene segments). Despite the junctional hypervariability, however, almost all functional V beta-D beta-J beta junctions appear to encode a glycine-containing beta-turn. Such a turn may serve to position the amino acid side chains of a hypervariable TCR beta-chain loop with respect to the antigen-binding groove of the major histocompatibility complex molecule. Consistent with this hypothesis, the germ-line D beta nucleotide sequences of chickens, mice, rabbits, and humans have been highly conserved and encode a glycine in all three reading frames.
authors.affiliation: Howard Hughes Medical Institute, Department of Internal Medicine, University of Michigan Medical School, Ann Arbor 48109.
authors.forename: W T
authors.initials: WT
authors.lastname: McCormack
authors.forename: L W
authors.initials: LW
authors.lastname: Tjoelker
authors.forename: G
authors.initials: G
authors.lastname: Stella
authors.forename: C E
authors.initials: CE
authors.lastname: Postema
authors.forename: C B
authors.initials: CB
authors.lastname: Thompson
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001665:Binding Sites; D005075:Biological Evolution; D002642:Chick Embryo; D002645:Chickens; D015333:Gene Rearrangement, beta-Chain T-Cell Antigen Receptor; D014644:Genetic Variation; D005998:Glycine; D008285:Major Histocompatibility Complex; D008969:Molecular Sequence Data; D015345:Oligonucleotide Probes; D011487:Protein Conformation; D011948:Receptors, Antigen, T-Cell / Q000235:genetics*; D012689:Sequence Homology, Nucleic Acid
chemical_list: D015345:Oligonucleotide Probes; D011948:Receptors, Antigen, T-Cell; D005998:Glycine