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Title: Direct single-molecule measurements of phycocyanobilin photophysics in monomeric C-phycocyanin

Phycobilisomes are highly organized pigment-protein antenna complexes found in the photosynthetic apparatus of cyanobacteria and rhodophyta that harvest solar energy and transport it to the reaction center. A detailed bottom-up model of pigment organization and energy transfer in phycobilisomes is essential to understanding photosynthesis in these organisms, and informing rational design of artificial light-harvesting systems. Particularly, heterogeneous photophysical behaviors of these proteins, which cannot be predicted de novo, may play an essential role in rapid light adaptation and photoprotection. Furthermore, the delicate architecture of these pigment-protein scaffolds sensitizes them to external perturbations, e.g: surface attachment, which can be avoided by study in free solution or in vivo. We present the first single-molecule characterization of C-phycocyanin (C-PC), a three-pigment biliprotein that self-assembles to form the mid-antenna rods of cyanobacterial phycobilisomes. Using the Anti-Brownian Electrokinetic (ABEL) trap to counteract Brownian motion of single particles in real-time, we directly monitor the changing photophysical states of individual C-PC monomers from Spirulina platensis in free solution by simultaneous readout of their brightness, fluorescence anisotropy, fluorescence lifetime, and emission spectra. These include single-chromophore emission states for each of the three covalently bound phycocyanobilins, providing the first direct measurement of the spectra and photophysics of these chemicallymore » identical molecules in their native protein environment. We also further show that a simple Förster Resonant Energy Transfer (FRET) network model accurately predicts the observed photophysical states of C-PC, and suggests highly variable quenching behavior of one of the chromophores, which should inform future studies of higher-order complexes.« less
 [1] ;  [1]
  1. Stanford Univ., CA (United States). Dept. of Chemistry
Publication Date:
Grant/Contract Number:
Published Article
Journal Name:
Proceedings of the National Academy of Sciences of the United States of America
Additional Journal Information:
Journal Volume: 114; Journal Issue: 37; Journal ID: ISSN 0027-8424
National Academy of Sciences, Washington, DC (United States)
Research Org:
Stanford Univ., CA (United States). Dept. of Chemistry
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; 59 BASIC BIOLOGICAL SCIENCES; photosynthetic protein; C-phycocyanin; ABEL trap; single-molecule spectroscopy; photodynamics
OSTI Identifier:
Alternate Identifier(s):
OSTI ID: 1377406