Ig from Trematomus bernacchii: a model for structural analysis of Ig from a cold adapted species

The immunoglobulin of the Antarctic teleost Trematomus bernacchii was inves tigated with respect to the amino acid sequence of the heavy chain and the diversity of the gene segments encoding the variable domain. A cDNA express ion library was constructed from the spleen and immunoscreened with rabbit anti-T. bernacchii IgH. A positive clone, found to encode the complete IgH sequence, including the leader peptide, was sequenced. Comparison of the de duced amino acid sequence of T. bernacchii constant domains with those from other actinopterygians showed identities ranging between 53.1 and 71.1%. M ultiple sequence alignment revealed the pressure of two remarkable insertio ns occurring in the VH-CH1 switch region and at the CH2-CH3 boundary. Addit ional differences were found in the number and positions of putative N-glyc osylation sites as well as of cysteine residues not involved in the intrado main bridges. An oligonucleotide primer was designed to amplify in PCR cDNA encoding different variable domains. The nucleotide sequence of 33 VH clon es was determined, and found distributed over three gene families, named Tr be VH I, Trbe VH II, and Trbe VH III. Nine distinct JH gene segments were a lso identified. The differences found with respect to other fish Ig, as wel l as the low diversity found in VH genes, were attributed to adaptation pro cesses.