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Proc Natl Acad Sci U S A. 2015 Jan 20;112(3):737-42. doi: 10.1073/pnas.1422272112. Epub 2015 Jan 5.

Flies expand the repertoire of protein structures that bind ice.

Author information

1
Protein Function Discovery Group and Department of Biomedical and Molecular Sciences, Queen's University, Kingston, ON, Canada K7L 3N6.
2
Protein Function Discovery Group and Department of Biomedical and Molecular Sciences, Queen's University, Kingston, ON, Canada K7L 3N6 peter.davies@queensu.ca.

Abstract

An antifreeze protein (AFP) with no known homologs has been identified in Lake Ontario midges (Chironomidae). The midge AFP is expressed as a family of isoforms at low levels in adults, which emerge from fresh water in spring before the threat of freezing temperatures has passed. The 9.1-kDa major isoform derived from a preproprotein precursor is glycosylated and has a 10-residue tandem repeating sequence xxCxGxYCxG, with regularly spaced cysteines, glycines, and tyrosines comprising one-half its 79 residues. Modeling and molecular dynamics predict a tightly wound left-handed solenoid fold in which the cysteines form a disulfide core to brace each of the eight 10-residue coils. The solenoid is reinforced by intrachain hydrogen bonds, side-chain salt bridges, and a row of seven stacked tyrosines on the hydrophobic side that forms the putative ice-binding site. A disulfide core is also a feature of the similar-sized beetle AFP that is a β-helix with seven 12-residue coils and a comparable circular dichroism spectrum. The midge and beetle AFPs are not homologous and their ice-binding sites are radically different, with the latter comprising two parallel arrays of outward-pointing threonines. However, their structural similarities is an amazing example of convergent evolution in different orders of insects to cope with change to a colder climate and provide confirmation about the physical features needed for a protein to bind ice.

KEYWORDS:

antifreeze protein; convergent evolution; disulfide-rich; midge; solenoid

PMID:
25561557
PMCID:
PMC4311821
DOI:
10.1073/pnas.1422272112
[Indexed for MEDLINE]
Free PMC Article

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