Fluorous Proteins

Towards the non-stick egg!

Perfluorocarbons exhibit unique and valuable physical properties that are not found in Nature. The best known example is Teflon®; in which the highly chemically inert and non-stick nature of this material derives from the perfluorinated polymer, polytetrafluoroethylene. We are exploring whether some of the properties that fluorine confers upon materials like Teflon might be transferred into proteins to produce biological molecules with novel and useful properties. In particular, such proteins are predicted to have enhanced thermal and chemical stabilities, and may eventually find uses as probes of cellular function and as diagnostic tools.

Towards novel bio-inspired materials

Our future goals are to use the knowledge gained from these experiments to aid in the design very small, stably folded proteins and to explore whether the fluorous effect can be used to engineer specific protein:protein interactions. We are also investigating whether fluorous amino acids can be used to enhance the biological activity of various bio-active peptides such as antimicrobial peptides, that show promise as therapeutic agents.

We have synthesized a series of 4-helix bundle proteins with increasing numbers of hexafluoroleucine residues in their hydrophobic cores that we call the a₄-F series. We found that the stability of these proteins, as represented by the free energy of unfolding, increases in direct proportion to the number of hexafluoroleucine residues incorporated. These proteins are also more stable to degradation by proteases, which is potentially a very useful property. Unexpectedly, incorporating fluorous residues appears to result in proteins that are better structured than the non-fluorinated parent protein, as judged by 2-D NMR experiments and F-19 NMR.

De novo design of fluorinated proteins

As a starting point for the construction of “Teflon” proteins, we are using short peptides that are designed to assemble into 4-alpha-helix bundle proteins, a commonly found protein structure in Nature. These proteins can be designed using a simple “helical wheel” template in which the pattern of amino acid interactions repeats every seven residues. The hydrophobic core can be packed in a simple, regular fashion with hydrophobic amino acids such as leucine. We have examined the effect of with replacing the hydrophobic core of our proteins with the extensively fluorinated (fluorous) analog of leucine, hexafluoroleucine, thereby creating a protein with a “Teflon-like” interior. To facilitate this work we have developed a highly efficient synthesis of hexa-fluoroleucine.

2-D NMR spectra suggest that the fluorinated protein (blue peaks) is better structured than its non-fluorinated counterpart (red peaks)