A DESIGNED HETEROTRIMERIC COILED-COIL

Principles that guide folding of coiled coils were tested by designing three peptides that preferentially associate with each other to form a heterotrimeric coiled coil. The core positions of the designed helic es contained residues that promote formation of trimeric coiled coils. Ionic interactions were employed to mediate heterospecificity, and ne gative design was used to favor formation of the heterotrimer over alt ernative arrangements. A program was written to select sequences that maximized the number of attractive interhelical interactions in a para llel heterotrimer and the number of repulsive electrostatic interactio ns in alternative species. Solution studies indicate that an equimolar mixture of the three peptides forms a helical trimer with high specif icity and stability. These results validate the principles used to gui de the design and suggest that the heterotrimer may serve as a useful, autonomous trimerization domain.