Why a Single Mutation Dims the Light: Local Chromophore Organization Modulates Fluorescence in smURFP
Noureen Abdelrahman1, Ding Ma1, Campbell Ruffing1
1Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina27599, United States.
Journal of Chemical Theory and Computation
|July 22, 2026
Summary
Predicting changes in fluorescent proteins is hard. A single mutation in smURFP alters chromophore orientation, affecting its fluorescence through local steric and electrostatic changes, not global rigidification.
Area of Science:
- Biophysics
- Structural Biology
- Computational Chemistry
Background:
- Predicting mutation effects on photophysical properties of bilin-binding fluorescent proteins is challenging.
- Understanding these changes is crucial for developing novel fluorescent probes.
Purpose of the Study:
- Investigate the origin of fluorescence modulation in smURFP and its Y56R variant.
- Elucidate the role of chromophore binding and protein structure in photophysical changes.
Main Methods:
- Classical Molecular Dynamics (MD) simulations.
- Quantum Mechanics/Molecular Mechanics (QM/MM) calculations.
- Analysis of chromophore binding states and protein pocket plasticity.
Main Results:
- The wild-type smURFP exhibits A-ring attachment and chromophore reduction.
- The Y56R variant shows an opposite chromophore orientation, indicating significant pocket plasticity.
- Differences in fluorescence and absorption are attributed to local steric and electrostatic redistribution, not global rigidification.
Conclusions:
- Single mutations can drastically alter biliprotein photophysics by modulating chromophore orientation and local environment.
- Spatially resolved descriptors from MD simulations offer mechanistic insights into biliprotein photophysics.
- This work provides a framework for understanding and engineering fluorescent proteins.
