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Updated: Jul 15, 2026
09:43
Identification of Plant Ice-binding Proteins Through Assessment of Ice-recrystallization Inhibition and Isolation Using Ice-affinity Purification
Published on: May 5, 2017
Evolution of hyperactive, repetitive antifreeze proteins in beetles
Laurie A Graham1, Wensheng Qin, Stephen C Lougheed
1Department of Biochemistry, Queen's University, Kingston, Ontario, Canada.
Journal of Molecular Evolution
|April 20, 2007
Summary
Mealworm beetles produce potent antifreeze proteins (AFPs) that prevent ice crystal growth. This study reveals variations in AFP gene structure and evolution in Tenebrio molitor, suggesting recombination and gene duplication/loss events.
Area of Science:
- Biochemistry
- Molecular Biology
- Evolutionary Biology
Background:
- Organisms like insects, fish, bacteria, and plants synthesize antifreeze proteins (AFPs) to survive subzero temperatures.
- AFPs adsorb to ice crystals, inhibiting their growth, with many AFPs exhibiting repetitive sequences and structures encoded by multigene families.
- Mealworm beetle (Tenebrio molitor) AFPs are highly effective, inhibiting ice growth below -5°C and featuring a 12-amino acid repeat forming a beta-helix structure.
Purpose of the Study:
- To investigate the cDNA and genomic sequences of additional Tenebrio molitor antifreeze protein (AFP) isoforms.
- To analyze the evolutionary mechanisms, including recombination, gene duplication, and amplification, that shape AFP gene families in T. molitor.
- To re-evaluate the selective pressures acting on T. molitor AFP genes, particularly concerning positive Darwinian selection versus AT content selection.
Main Methods:
- Obtained cDNA and genomic sequences of T. molitor AFP isoforms.
- Analyzed sequence variations, focusing on the number of 12-amino acid repeats.
- Performed phylogenetic comparisons of AFPs from T. molitor and Dendroides canadensis.
- Calculated the ratio of nonsynonymous-to-synonymous substitutions.
Main Results:
- Identified T. molitor AFP isoforms with varying repeat numbers (6 to 10), largely attributable to recombination at TCT motifs.
- Phylogenetic analysis suggests gene loss and amplification events occurred post-species divergence between T. molitor and D. canadensis.
- The observed high ratio of nonsynonymous-to-synonymous substitutions is proposed to result from selection for higher AT content at the third codon position, rather than positive Darwinian selection.
Conclusions:
- Recombination at TCT motifs is a significant mechanism driving variation in T. molitor AFP repeat numbers.
- Gene duplication and loss have played roles in the evolution of AFP gene families in mealworm beetles.
- Selection for increased AT content in the third codon position may explain the observed substitution patterns in T. molitor AFPs.
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