OBSERVATION OF A SILK-LIKE CRYSTAL-STRUCTURE IN A GENETICALLY-ENGINEERED PERIODIC POLYPEPTIDE

A genetically engineered periodic polypeptide consisting of 36 repeats of the octapeptide sequence -(AlaGly)(3)GluGly- has been crystallized from solution in aqueous lithium bromide. Analysis by solid-state nuc lear magnetic resonance spectroscopy, vibrational spectroscopy, and wi de-angle x-ray diffraction reveals a crystal structure analogous to th at obtained when silk solutions are allowed to dry under quiescent con ditions, i.e., the silk I structure. Previous analyses of the same pol ymer have demonstrated an antiparallel beta-sheet architecture (silk I I structure) in samples crystallized from formic acid. These results i llustrate the potential for controlling the solid-state structures and properties of genetically engineered materials through selection of a ppropriate processing and crystallization conditions.