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Serpins in unicellular Eukarya, Archaea, and Bacteria: sequence analysis and evolution.

Thomas H Roberts1, Jorn Hejgaard, Neil F W Saunders

  • 1Department of Biological Sciences, Macquarie University, NSW 2109, Australia. troberts@els.mq.edu.au

Journal of Molecular Evolution
|January 11, 2005
PubMed
Summary

This study reveals that serpins (serine protease inhibitors) in unicellular eukaryotes possess distinct characteristics from those in higher organisms. These findings shed light on the early evolution of serpins and their potential inhibitory functions across diverse life forms.

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Area of Science:

  • Biochemistry
  • Evolutionary Biology
  • Genomics

Background:

  • Serpins are proteins that inactivate serine proteinases, with animal serpins regulating diverse metabolic processes.
  • The evolutionary origins and functions of serpins outside of animals remain largely unknown.
  • The native structure of inhibitory serpins is metastable, requiring rapid conversion to trap target enzymes.

Purpose of the Study:

  • To investigate the evolutionary origin and functional characteristics of serpin genes in unicellular eukaryotes.
  • To compare serpins from unicellular organisms with those found in prokaryotes and higher eukaryotes.
  • To understand the early diversification and potential roles of serpins in life's history.

Main Methods:

  • Bioinformatic analysis of serpin genes from selected unicellular eukaryotes (Chlamydomonas reinhardtii, Alexandrium tamarense, Entamoeba spp., Eimeria tenella, Toxoplasma gondii, Giardia lamblia).

Related Experiment Videos

  • Comparative sequence analysis of identified serpins against archaeal and bacterial serpin sequences.
  • Phylogenetic analysis to determine evolutionary relationships.
  • Examination of conserved residues, particularly at the reactive-center loop and P1 position, to infer function.

    • Main Results:

    • Serpins were identified in unicellular eukaryotes, Archaea, and Bacteria, with distinct phylogenetic distributions.
    • Unicellular eukaryotic serpins appear phylogenetically distinct from higher eukaryotic serpins.
    • Most unicellular serpins exhibit characteristics of inhibitory serpins, including specific residues at the P1 position.
    • Prokaryotic serpins generally lack these specific P1 residues, suggesting functional divergence.

    Conclusions:

    • Serpins have a deep evolutionary history, predating the divergence of eukaryotes and prokaryotes.
    • Unicellular eukaryotes possess unique serpin repertoires that differ from those in animals.
    • The identified serpin characteristics in unicellular organisms provide insights into early serpin evolution and function.