Chapter 83 - Ultrafast excited state dynamics in the green fluorescent protein chromophore

Abstract

The textbook picture of photo-induced cis-trans isomerization in unsaturated hydrocarbons is one-dimensional, focusing on simple torsion about a C=C bond. The resulting large amplitude motion seems inconsistent with the steric constraints imposed by protein environments. This observation led to many proposals for minimal-volume photoisomerization pathways in protein environments. Recent work has shown that the mechanism for photoisomerization is considerably more complicated than simple torsion, implying that the inconsistency mentioned above may be only apparent. In fact, photoisomerization often involves both torsion and pyramidalization, leading to excited state dynamics much more akin to a “slicing” motion as opposed to the “sweeping” motion most naturally envisioned for a simple torsion. Thus, the question is to what extent the protein environment modifies the photochemical reaction pathway associated with photoisomerization. This chapter discusses theoretical studies of photoisomerization in the chromophore of green fluorescent protein (GFP).