Duplication of a Single Strand in a ß-Sheet Can Produce a New Switching Function in a Photosensory Protein.

ABSTRACT

Duplication of a single ß-strand that forms part of a ß-sheet in photoactive yellow protein (PYP) was found to produce two approximately isoenergetic protein conformations, in which either the first or the second copy of the duplicated ß-strand participates in the ß-sheet. Whereas one conformation (big-loop) is more stable at equilibrium in the dark, the other conformation (long-tail) is populated after recovery from blue light irradiation. By appending a recognition motif (E-helix) to the C-terminus of the protein, we show that ß-strand duplication, and the resulting possibility of ß-strand slippage, can lead to a new switchable protein-protein interaction. We suggest that ß-strand duplication may be a general means of introducing two-state switching activity into protein structures.