Comparison of the structures and stabilities of coiled-coil proteins containing hexafluoroleucine and t-butylalanine provides insight into the stabilizing effects of highly fluorinated amino acid side-chains

Authors

  • Benjamin C. Buer,

    1. Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48109
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  • Jennifer L. Meagher,

    1. Life Sciences Institute, University of Michigan, Ann Arbor, Michigan 48109
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  • Jeanne A. Stuckey,

    1. Life Sciences Institute, University of Michigan, Ann Arbor, Michigan 48109
    2. Department of Biological Chemistry, University of Michigan Medical School, Ann Arbor, Michigan 48109
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  • E. Neil G. Marsh

    Corresponding author
    1. Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48109
    2. Department of Biological Chemistry, University of Michigan Medical School, Ann Arbor, Michigan 48109
    • Department of Chemistry, University of Michigan, Ann Arbor, MI 48109
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  • The coordinates of the proteins described in this study have been deposited in the protein data bank with PDB IDs:α4F3d: 4G3B; α4F3(6-13): 4G4M; α4tbA6: 4G4L

Abstract

Highly fluorinated analogs of hydrophobic amino acids are well known to increase the stability of proteins toward thermal unfolding and chemical denaturation, but there is very little data on the structural consequences of fluorination. We have determined the structures and folding energies of three variants of a de novo designed 4-helix bundle protein whose hydrophobic cores contain either hexafluoroleucine (hFLeu) or t-butylalanine (tBAla). Although the buried hydrophobic surface area is the same for all three proteins, the incorporation of tBAla causes a rearrangement of the core packing, resulting in the formation of a destabilizing hydrophobic cavity at the center of the protein. In contrast, incorporation of hFLeu, causes no changes in core packing with respect to the structure of the nonfluorinated parent protein which contains only leucine in the core. These results support the idea that fluorinated residues are especially effective at stabilizing proteins because they closely mimic the shape of the natural residues they replace while increasing buried hydrophobic surface area.

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