Journal of Molecular Evolution

, Volume 34, Issue 6, pp 536–543

Evolutionary origin of a Kunitz-type trypsin inhibitor domain inserted in the amyloid β precursor protein of Alzheimer's disease

Authors

  • Kazuho Ikeo
    • DNA Research CenterNational Institute of Genetics
    • The Graduate University for Advanced Studies
  • Kei Takahashi
    • Department of PhysiologyShimane Medical University
  • Takashi Gojobori
    • DNA Research CenterNational Institute of Genetics
Article

DOI: 10.1007/BF00160466

Cite this article as:
Ikeo, K., Takahashi, K. & Gojobori, T. J Mol Evol (1992) 34: 536. doi:10.1007/BF00160466

Summary

The Kunitz-type protease inhibitor is one of the serine protease inhibitors. It is found in blood, saliva, and all tissues in mammals. Recently, a Kunitz-type sequence was found in the protein sequence of the amyloid β precursor protein (βAPP). It is known that βAPP accumulates in the neuritic plaques and cerebrovascular deposits of patients with Alzheimer's disease. Collagen type VI in chicken also has an insertion of a Kunitz-type sequence. To elucidate the evolutionary origin of these insertion sequences, we constructed a phylogenetic tree by use of all the available sequences of Kunitz-type inhibitors. The tree shows that the ancestral gene of the Kunitz-type inhibitor appeared about 500 million years ago. Thereafter, this gene duplicated itself many times, and some of the duplicates were inserted into other protein-coding genes. During this process, the Kunitz-type sequence in the present βAPP gene diverged from its ancestral gene about 270 million years ago and was inserted into the gene soon after duplication. Although the function of the insertion sequences is unknown, our molecular evolutionary analysis shows that these insertion sequences in βAPP have an evolutionarily close relationship with the inter-α-trypsin inhibitor or trypstatin, which inhibits the activity of tryptase, a novel membrane-bound serine protease in human T4+ lymphocytes.

Key words

Serine protease inhibitorKunitz typeEvolutionary originAlzheimer's diseaseInsertion sequence
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Copyright information

© Springer-Verlag New York Inc 1992