Intermediate activity of midge antifreeze protein is due to a tyrosine-rich ice-binding site and atypical ice plane affinity.

Autor: Basu K; Protein Function Discovery Group, Department of Biomedical and Molecular Sciences, Queen's University, Kingston, Canada., Wasserman SS; Department of Biochemistry, Programme in Cell Biology, Hospital for Sick Children, University of Toronto, Canada., Jeronimo PS; Protein Function Discovery Group, Department of Biomedical and Molecular Sciences, Queen's University, Kingston, Canada., Graham LA; Protein Function Discovery Group, Department of Biomedical and Molecular Sciences, Queen's University, Kingston, Canada., Davies PL; Protein Function Discovery Group, Department of Biomedical and Molecular Sciences, Queen's University, Kingston, Canada.
Jazyk: angličtina
Zdroj: The FEBS journal [FEBS J] 2016 Apr; Vol. 283 (8), pp. 1504-15. Date of Electronic Publication: 2016 Mar 11.
DOI: 10.1111/febs.13687
Abstrakt: Unlabelled: An antifreeze protein (AFP) from a midge (Chironomidae) was recently discovered and modelled as a tightly wound disulfide-braced solenoid with a surface-exposed rank of stacked tyrosines. New isoforms of the midge AFP have been identified from RT-PCR and are fully consistent with the model. Although they differ in the number of 10-residue coils, the row of tyrosines that form the putative ice-binding site is conserved. Recombinant midge AFP has been produced, and the properly folded form purified by ice affinity. This monomeric AFP has a distinct circular dichroism spectrum, a melting temperature between 35 and 50 °C and is fully renaturable on cooling. Mutagenesis of the middle tyrosine in the rank of seven eliminates antifreeze activity, whereas mutation of a tyrosine off this predicted ice-binding face had no such effect. This AFP has unusual properties compared to other known AFPs. First, its freezing-point depression activity is intermediate between that of the hyperactive and moderately active AFPs. As with hyperactive AFPs, when midge AFP-bound ice crystals exceed their freezing-point depression, ice grows explosively perpendicular to the c-axis. However, midge AFP does not bind to the basal plane of ice as do hyperactive AFPs, but rather to a pyramidal plane that is at a shallower angle relative to the basal plane than binding planes of moderate AFPs. These properties distinguish midge AFP from all other ice-binding proteins and the intermediate activity level fits well to the modest challenge of protecting newly emerged adult insects from late spring frosts.
Database: Nucleotide sequences of new midge AFP isoforms are available in the GenBank database under accession numbers KU094814-8. Sequences will be released after publication.
(© 2016 Federation of European Biochemical Societies.)
Databáze: MEDLINE
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