Cloning and modeling of CD8 beta in the amphibian ambystoma Mexicanum. Evolutionary conserved structures for interactions with major histocompatibility complex (MHC) class I molecules.
Mammalian and avian T-cells exhibit a large number of well characterized surface molecules associated with their maturation degree. Very little is known in comparison with T-cell differentiation in ectothermic vertebrates. This is mainly due to the lack of probes to identify T-cell subsets. We cloned and sequenced the first ectothermic CD8 beta DNA complementary to RNA from an amphibian species, the Mexican axolotl. The CD8 beta chain was 30-36% identical with its avian and mammalian homologues. The extracellular V-like domain contained the two typically conserved cysteines and was followed by a J-like sequence containing the canonical Phe-Gly-X-Gly stretch. The connecting peptide was much longer than in other species and contained potential O-glycosylation sites. The axolotl CD8 beta and major histocompatibility complex class I molecules were modeled using human HLA-A2/CD8 alphaalpha complex as template. The backbone conformation of axolotl CD8 beta matched well with the CD8 alpha-2 subunit of the human complex but significant structural differences were located in the CDR1, CDR2 and DE loops. Both axolotl and human class I showed large negative surface potential. The interacting area of the human CD8 alpha chain and of the corresponding region of axolotl CD8 beta had positive electrostatic potential compatible with complexation with the corresponding class I molecules. The presence of a CD8 beta homologue in an amphibian species implies that it was already present in the Devonian ancestor of amphibians and mammals, i.e. more than 400 million years ago.
Fellah
Julien S
JS
Laboratoire de Biologie Cellulaire et Moléculaire du Développement, Equipe d'Immunologie Comparée, CNRS UMR 7622, Université Pierre et Marie Curie, 9 quai Saint-Bernard, boîte 24, 75252, Paris Cedex 05, France. jsfellah@snv.jussieu.fr
Tuffèry
Pierre
P
Etchebest
Catherine
C
Guillet
Françoise
F
Bleux
Christian
C
Charlemagne
Jacques
J
D000558:Ambystoma mexicanum / Q000235:genetics*; D000595:Amino Acid Sequence; D000818:Animals; D016827:CD8 Antigens / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000737:chemistry / Q000235:genetics; D019143:Evolution, Molecular; D015870:Gene Expression; D015395:Histocompatibility Antigens Class I / Q000378:metabolism; D017403:In Situ Hybridization; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D021122:Protein Subunits; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid
D016827:CD8 Antigens; D018076:DNA, Complementary; D015395:Histocompatibility Antigens Class I; D021122:Protein Subunits; D012333:RNA, Messenger