AN EVOLUTIONARY APPROACH TO FOLDING SMALL ALPHA-HELICAL PROTEINS THAT USES SEQUENCE INFORMATION AND AN EMPIRICAL GUIDING FITNESS FUNCTION

Three short protein sequences have been guided by computer to folds resembling their crystal structures. Initially, peptide fragment conformations ranging in size from 9 to 25 residues were selected from a database of known protein structures. A fragment was selected if it was compatible with a segment of the sequence to be folded, as judged by three-dimensional profile scores. By linking the selected fragment conformations together, hundreds of trial structures were generated of the same length and sequence as the protein to be folded. These starting trial structures were then improved by an evolutionary algorithm. Selection pressure for improving the structures was provided by an energy function that was designed to guide the conformational search procedure toward the correct structure. We find that by evolution of only 400 structures for fewer than 1400 generations, the overall fold of some small helical proteins can be computed from the sequence, with deviations from observed structures of 2.5-4.0 Angstrom for C alpha atoms.