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J Pharm Sci. 2016 Apr;105(4):1444-53. doi: 10.1016/j.xphs.2016.02.010.

Engineering a Cysteine-Free Form of Human Fibroblast Growth Factor-1 for "Second Generation" Therapeutic Application.

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Department of Biomedical Sciences, Florida State University, Tallahassee, Florida 32306.
Department of Pharmaceutical Chemistry, University of Kansas, Lawrence, Kansas 66047.
Department of Developmental Biology, Washington University School of Medicine, St. Louis, Missouri 63110.
Department of Biomedical Sciences, Florida State University, Tallahassee, Florida 32306. Electronic address:


Human fibroblast growth factor-1 (FGF-1) has broad therapeutic potential in regenerative medicine but has undesirable biophysical properties of low thermostability and 3 buried cysteine (Cys) residues (at positions 16, 83, and 117) that interact to promote irreversible protein unfolding under oxidizing conditions. Mutational substitution of such Cys residues eliminates reactive buried thiols but cannot be accomplished simultaneously at all 3 positions without also introducing further substantial instability. The mutational introduction of a novel Cys residue (Ala66Cys) that forms a stabilizing disulfide bond (i.e., cystine) with one of the extant Cys residues (Cys83) effectively eliminates one Cys while increasing overall stability. This increase in stability offsets the associated instability of remaining Cys substitution mutations and permits production of a Cys-free form of FGF-1 (Cys16Ser/Ala66Cys/Cys117Ala) with only minor overall instability. The addition of a further stabilizing mutation (Pro134Ala) creates a Cys-free FGF-1 mutant with essentially wild-type biophysical properties. The elimination of buried free thiols in FGF-1 can substantially increase the protein half-life in cell culture. Here, we show that the effective cell survival/mitogenic functional activity of a fully Cys-free form is also substantially increased and is equivalent to wild-type FGF-1 formulated in the presence of heparin sulfate as a stabilizing agent. The results identify this Cys-free FGF-1 mutant as an advantageous "second generation" form of FGF-1 for therapeutic application.


FGF-1; X-ray crystallography; cysteine-free mutant; cystine; disulfide; empirical phase diagram; protein engineering; protein stability

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