STRUCTURAL AND DYNAMIC CHANGES OF PHOTOACTIVE YELLOW PROTEIN DURING ITS PHOTOCYCLE IN SOLUTION

Light irradiation of photoactive yellow protein (PYP) induces a photoc ycle, in which red-shifted (pR) and blue-shifted (pB) intermediates ha ve been characterized. An NMR study of the long-lived pB intermediate now reveals that it exhibits a large degree of disorder and exists as a family of multiple conformers that exchange on a millisecond time sc ale. This shows that the behavior of PYP in solution is different from what has been observed in the crystalline state. Furthermore, differe ntial refolding to ground state pG is observed, whereby the central be ta-sheet and parts of the helical structure are formed first and the r egion around the chromophore at a later stage.