Direct observation and pH control of reversed supramolecular chirality in insulin fibrils by vibrational circular dichroism.

The controlled reversal of supramolecular helical chirality in protein fibrils is reported for the first time. Normal or reversed insulin fibrils were grown by precise adjustment of pH. AFM images show two polymorphs corresponding to opposite senses of helical twist of the supramolecular structure with the same cross-β-sheet core.