Evolution of vertebrate IgM: complete amino acid sequence of the constant region of Ambystoma mexicanum μ chain deduced from cDNA sequence

✍ Scribed by Julien S. Fellah; Michael V. Wiles; Jacques Charlemagne; Joseph Schwager

• Publisher: John Wiley and Sons
• Year: 1992
• Tongue: English
• Weight: 763 KB
• Volume: 22
• Category: Article
• ISSN: 0014-2980
• DOI: 10.1002/eji.1830221019

✦ Synopsis

Evolution of vertebrate IgM: complete amino acid sequence of the constant region of Ambystoma mexicanum p chain deduced from cDNA sequence* cDNA clones coding for the constant region of the Mexican axolotl (Ambystoma mexicanum) p heavy immunoglobulin chain were selected from total spleen RNA, using a cDNA polymerase chain reaction technique. The specific 5'-end primer was an oligonucleotide homologous to the JH segment of Xenopus laevis p chain. One of the clones, JHAM, corresponded to the complete constant region of the axolotl p chain, consisting of a 1362-nucleotide sequence coding for a polypeptide of 454 amino acids followed in 3' direction by a 179-nucleotide untranslated region and a polyA+ tail. The axolotl C, is divided into four typical domains (C,l-C,4) and can be aligned with the Xenopus C, with an overall identity of 56% at the nucleotide level. Percent identities were particularly high between C,1(59%) and C,4 (71%).The C-terminal20-amino acid segment which constitutes the secretory part of the p chain is strongly homologous to the equivalent sequences of chondrichthyans and of other tetrapods, including a conserved N-linked oligosaccharide, the penultimate cysteine and the C-terminal lysine. The four C,, domains of 13 vertebrate species ranging from chondrichthyans to mammals were aligned and compared at the amino acid level. The significant number of p-specific residues which are conserved into each of the four C, domains argues for a continuous line of evolution of the vertebrate p chain. This notion was confirmed by the ability to reconstitute a consistent vertebrate evolution tree based on the phylogenic parsimony analysis of the C,4 sequences.