title: Symmetric primary and tertiary structure mutations within a symmetric superfold: a solution, not a constraint, to achieve a foldable polypeptide.
abstract: In previous studies designed to increase the primary structure symmetry within the hydrophobic core of human acidic fibroblast growth factor (FGF-1) a combination of five mutations were accommodated, resulting in structure, stability and folding kinetic properties similar to wild-type (despite the symmetric constraint upon the set of core residues). A sixth mutation in the core, involving a highly conserved Met residue at position 67, appeared intolerant to substitution. Structural analysis suggested that the local packing environment of position 67 involved two regions of apparent insertions that distorted the tertiary structure symmetry inherent in the beta-trefoil architecture. It was postulated that a symmetric constraint upon the primary structure within the core could only be achieved after these insertions had been deleted (concomitantly increasing the tertiary structure symmetry). The deletion of these insertions is now shown to permit mutation of position 67, thereby increasing the primary structure symmetry relationship within the core. Furthermore, despite the imposed symmetric constraint upon both the primary and tertiary structure, the resulting mutant form of FGF-1 is substantially more stable. The apparent inserted regions are shown to be associated with heparin-binding functionality; however, despite a marked reduction in heparin-binding affinity the mutant form of FGF-1 is surprisingly approximately 70 times more potent in 3T3 fibroblast mitogenic assays. The results support the hypothesis that primary structure symmetry within a symmetric protein superfold represents a possible solution, rather than a constraint, to achieving a foldable polypeptide.
authors.affiliation: Kasha Laboratory, Institute of Molecular Biophysics and Department of Chemistry and Biochemistry, Florida State University, Tallahassee, FL 32306-4380, USA.
authors.forename: Stephen R
authors.initials: SR
authors.lastname: Brych
authors.forename: Vikash K
authors.initials: VK
authors.lastname: Dubey
authors.forename: Ewa
authors.initials: E
authors.lastname: Bienkiewicz
authors.forename: Jihun
authors.initials: J
authors.lastname: Lee
authors.forename: Timothy M
authors.initials: TM
authors.lastname: Logan
authors.forename: Michael
authors.initials: M
authors.lastname: Blaber
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002151:Calorimetry; D016220:Fibroblast Growth Factor 1 / Q000737:chemistry* / Q000235:genetics; D007700:Kinetics; D051379:Mice; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016296:Mutagenesis; D041681:NIH 3T3 Cells; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D017386:Sequence Homology, Amino Acid; D013816:Thermodynamics
chemical_list: D016220:Fibroblast Growth Factor 1