Positive Darwinian Selection Promotes Heterogeneity Among Members of the Antifreeze Protein Multigene Family |
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Authors: | Willie J Swanson Charles F Aquadro |
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Institution: | (1) Department of Biology, University of California, Riverside, Riverside, CA 92521, USA, US;(2) Department of Molecular Biology and Genetics, 402 Biotechnology Building, Cornell University, Ithaca, NY 14853-2703, USA, US |
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Abstract: | A variety of organisms have independently evolved proteins exhibiting antifreeze activity that allows survival at subfreezing
temperatures. The antifreeze proteins (AFPs) bind ice nuclei and depress the freezing point by a noncolligative absorption–inhibition
mechanism. Many organisms have a heterogeneous suite of AFPs with variation in primary sequence between paralogous loci. Here,
we demonstrate that the diversification of the AFP paralogues is promoted by positive Darwinian selection in two independently
evolved AFPs from fish and beetle. First, we demonstrate an elevated rate of nonsynonymous substitutions compared to synonymous
substitutions in the mature protein coding region. Second, we perform phylogeny-based tests of selection to demonstrate a
subset of codons is subjected to positive selection. When mapped onto the three-dimensional structure of the fish antifreeze
type III antifreeze structure, these codons correspond to amino acid positions that surround but do not interrupt the putative
ice-binding surface. The selective agent may be related to efficient binding to diverse ice surfaces or some other aspect
of AFP function.
Received: 27 February 2001 / Accepted: 12 September 2001 |
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Keywords: | : Antifreeze proteins — Darwinian selection — Likelihood ratio test — Adaptive evolution |
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