Journal of Molecular Evolution

, Volume 71, Issue 2, pp 111–118

Functional Diversification and Evolution of Antifreeze Proteins in the Antarctic Fish Lycodichthys dearborni

  • Joanna L. Kelley
  • Jan E. Aagaard
  • Michael J. MacCoss
  • Willie J. Swanson
Article

DOI: 10.1007/s00239-010-9367-6

Cite this article as:
Kelley, J.L., Aagaard, J.E., MacCoss, M.J. et al. J Mol Evol (2010) 71: 111. doi:10.1007/s00239-010-9367-6

Abstract

Antifreeze proteins (AFPs) have independently evolved in many organisms. AFPs act by binding to ice crystals, effectively lowering the freezing point. AFPs are often at high copy number in a genome and diversity exists between copies. Type III antifreeze proteins are found in Arctic and Antarctic eel pouts, and have previously been shown to evolve under positive selection. Here we combine molecular and proteomic techniques to understand the molecular evolution and diversity of Type III antifreeze proteins in a single individual Antarctic fish Lycodichthys dearborni. Our expressed sequence tag (EST) screen reveals that at least seven different AFP variants are transcribed, which are ultimately translated into five different protein isoforms. The isoforms have identical 66 base pair signal sequences and different numbers of subsequent ice-binding domains followed by a stop codon. Isoforms with one ice-binding unit (monomer), two units (dimer), and multiple units (multimer) were present in the EST library. We identify a previously uncharacterized protein dimer, providing further evidence that there is diversity between Type III AFP isoforms, perhaps driven by positive selection for greater thermal hysteresis. Proteomic analysis confirms that several of these isoforms are translated and present in the liver. Our molecular evolution study shows that paralogs have diverged under positive selection. We hypothesize that antifreeze protein diversity is an important contributor to depressing the serum freezing point.

Keywords

Antifreeze proteins Adaptive evolution Paralogs Isoforms Mass spectrometry Positive selection Type III AFPs 

Supplementary material

239_2010_9367_MOESM1_ESM.doc (608 kb)
Supplementary material 1 (DOC 608 kb)

Copyright information

© Springer Science+Business Media, LLC 2010

Authors and Affiliations

  • Joanna L. Kelley
    • 1
    • 2
  • Jan E. Aagaard
    • 1
  • Michael J. MacCoss
    • 1
  • Willie J. Swanson
    • 1
  1. 1.Department of Genome SciencesUniversity of WashingtonSeattleUSA
  2. 2.Department of Human GeneticsUniversity of ChicagoChicagoUSA

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