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Structural Evidence of Photoisomerization Pathways in Fluorescent Proteins

preprint
submitted on 01.08.2019 and posted on 02.08.2019 by Jeffrey Chang, Matthew Romei, Steven Boxer

Double-bond photoisomerization in molecules such as the green fluorescent protein (GFP) chromophore can occur either via a volume-demanding one-bond-flip pathway or via a volume-conserving hula-twist pathway. Understanding the factors that determine the pathway of photoisomerization would inform the rational design of photoswitchable GFPs as improved tools for super-resolution microscopy. In this communication, we reveal the photoisomerization pathway of a photoswitchable GFP, rsEGFP2, by solving crystal structures of cis and trans rsEGFP2 containing a monochlorinated chromophore. The position of the chlorine substituent in the trans state breaks the symmetry of the phenolate ring of the chromophore and allows us to distinguish the two pathways. Surprisingly, we find that the pathway depends on the arrangement of protein monomers within the crystal lattice: in a looser packing, the one-bond-flip occurs, whereas in a tighter packing (7% smaller unit cell size), the hula-twist occurs.

Funding

National Institutes of Health GM118044

History

Email Address of Submitting Author

jeffjar@stanford.edu

Institution

Stanford University

Country

United States

ORCID For Submitting Author

0000-0001-9342-5072

Declaration of Conflict of Interest

No conflict of interest

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