FROM COILED COILS TO SMALL GLOBULAR-PROTEINS - DESIGN OF A NATIVE-LIKE 3-HELIX BUNDLE

A monomolecular native-like three-helix bundle has been designed in an iterative process, beginning with a peptide that noncooperatively ass embled into an antiparallel three-helix bundle. Three versions of the protein were designed in which specific interactions were incrementall y added. The hydrodynamic and spectroscopic properties of the proteins were examined by size exclusion chromatography, sedimentation equilib rium, fluorescence spectroscopy, and NMR. The thermodynamics of foldin g were evaluated by monitoring the thermal and guanidine-induced unfol ding transitions using far UV circular dichroism spectroscopy. The att ainment of a unique, native-like state was achieved through the introd uction of: (1)helix capping interactions; (2) electrostatic interactio ns between partially exposed charged residues; (3) a diverse collectio n of apolar side chains within the hydrophobic core.