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Type II opsins: evolutionary origin by internal domain duplication?

Nicholas D Larusso1, Brian E Ruttenberg, Ambuj K Singh

  • 1Department of Computer Science, University of California, Santa Barbara, CA 93106, USA.

Journal of Molecular Evolution
|April 9, 2008
PubMed
Summary
This summary is machine-generated.

Type I and Type II opsins, proteins with seven transmembrane segments, evolved light sensitivity independently. This suggests a convergent evolutionary origin rather than shared ancestry for these opsin types.

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Area of Science:

  • Molecular Biology
  • Evolutionary Biology
  • Biochemistry

Background:

  • Opsins are proteins with seven transmembrane segments (TMSs) found across life.
  • Type I opsins are in prokaryotes/eukaryotes; Type II opsins are in animals and are G-protein coupled receptors (GPCRs).
  • Previous studies suggested internal domain duplication for some TMS proteins, including Type I opsins.

Purpose of the Study:

  • To investigate the evolutionary origin of Type II opsins.
  • To test if Type II opsins originated via internal domain duplication.
  • To provide evidence for or against the homology of Type I and Type II opsins.

Main Methods:

  • Comparative genomic analysis.
  • Phylogenetic analysis of opsin protein families.
  • Structural analysis of transmembrane proteins.

Main Results:

  • Type II opsins do not show evidence of originating from internal domain duplication.
  • This finding supports the hypothesis that Type I and Type II opsins are nonhomologous.
  • Both opsin types independently evolved a seven-TM structure and light sensitivity.

Conclusions:

  • Type I and Type II opsins likely represent a case of convergent evolution.
  • The independent evolution of light sensitivity in opsins highlights the functional importance of the seven-TM structure.
  • This convergence suggests a significant role for seven-TM protein architecture in retinal-based light detection.