Detection of gene duplication signals of Ig folds from their amino acid sequences.

Protein folds may evolve from short peptide ancestors via gene duplication and fusion. For proteins with internal structural symmetry, this means that their sequences should be made up of identical repeats. However, many of these repeat signals can only be seen at the structural level yet. Motivated by the fact that proteins may have similar structures if their sequences have more than 25% identical amino acids, we suggest a method to detect the sequence repeats of proteins directly from their sequences. Using this method, we show that the internal repetitions of the immunoglobulin folds could be identified directly at the sequence level.