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Title: Molecular mechanism of reflectin’s tunable biophotonic control: Opportunities and limitations for new optoelectronics

Abstract

Discovery that reflectin proteins fill the dynamically tunable Bragg lamellae in the reflective skin cells of certain squids has prompted efforts to design new reflectin-inspired systems for dynamic photonics. But new insights into the actual role and mechanism of action of the reflectins constrain and better define the opportunities and limitations for rationally designing optical systems with reflectin-based components. We and our colleagues have discovered that the reflectins function as a signal-controlled molecular machine, regulating an osmotic motor that tunes the thickness, spacing, and refractive index of the tunable, membrane-bound Bragg lamellae in the iridocytes of the loliginid squids. The tunable reflectin proteins, characterized by a variable number of highly conserved peptide domains interspersed with positively charged linker segments, are restricted in intra- and inter-chain contacts by Coulombic repulsion. Physiologically, this inhibition is progressively overcome by charge-neutralization resulting from acetylcholine (neurotransmitter)-induced, site-specific phosphorylation, triggering the simultaneous activation and progressive tuning of reflectance from red to blue. Details of this process have been resolved through in vitro analyses of purified recombinant reflectins, controlling charge-neutralization by pH-titration or mutation as surrogates for the in vivo phosphorylation. Results of these analyses have shown that neutralization overcoming the Coulombic inhibition reversibly and cyclably triggersmore » condensation and secondary folding of the reflectins, with the emergence of previously cryptic, phase-segregated hydrophobic domains enabling hierarchical assembly. This tunable, reversible, and cyclable assembly regulates the Gibbs-Donnan mediated osmotic shrinking or swelling of the Bragg lamellae that tunes the brightness and color of reflected light. Our most recent studies have revealed a direct relationship between the extent of charge neutralization and the size of the reflectin assemblies, further explaining the synergistic effects on the intensity and wavelength of reflected light. Mutational analyses show that the “switch” controlling reflectins’ structural transitions is distributed along the protein, while detailed comparisons of the sequences and structures of the recently evolved tunable reflectins to those of their ancestral, non-tunable homologs are helping to identify the specific structural determinants governing tunability.« less

Authors:
 [1];  [1];  [1]
  1. Univ. of California, Santa Barbara, CA (United States). Dept. of Molecular, Cellular and Developmental Biology and the Inst. for Collaborative Biotechnologies
Publication Date:
Research Org.:
Univ. of California, Santa Barbara, CA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22). Materials Sciences & Engineering Division; USDOE
OSTI Identifier:
1501519
Alternate Identifier(s):
OSTI ID: 1376760
Grant/Contract Number:  
SC0015472
Resource Type:
Accepted Manuscript
Journal Name:
APL Materials
Additional Journal Information:
Journal Volume: 5; Journal Issue: 10; Journal ID: ISSN 2166-532X
Publisher:
American Institute of Physics (AIP)
Country of Publication:
United States
Language:
English
Subject:
59 BASIC BIOLOGICAL SCIENCES; 47 OTHER INSTRUMENTATION

Citation Formats

Levenson, Robert, DeMartini, Daniel G., and Morse, Daniel E. Molecular mechanism of reflectin’s tunable biophotonic control: Opportunities and limitations for new optoelectronics. United States: N. p., 2017. Web. doi:10.1063/1.4985758.
Levenson, Robert, DeMartini, Daniel G., & Morse, Daniel E. Molecular mechanism of reflectin’s tunable biophotonic control: Opportunities and limitations for new optoelectronics. United States. doi:10.1063/1.4985758.
Levenson, Robert, DeMartini, Daniel G., and Morse, Daniel E. Thu . "Molecular mechanism of reflectin’s tunable biophotonic control: Opportunities and limitations for new optoelectronics". United States. doi:10.1063/1.4985758. https://www.osti.gov/servlets/purl/1501519.
@article{osti_1501519,
title = {Molecular mechanism of reflectin’s tunable biophotonic control: Opportunities and limitations for new optoelectronics},
author = {Levenson, Robert and DeMartini, Daniel G. and Morse, Daniel E.},
abstractNote = {Discovery that reflectin proteins fill the dynamically tunable Bragg lamellae in the reflective skin cells of certain squids has prompted efforts to design new reflectin-inspired systems for dynamic photonics. But new insights into the actual role and mechanism of action of the reflectins constrain and better define the opportunities and limitations for rationally designing optical systems with reflectin-based components. We and our colleagues have discovered that the reflectins function as a signal-controlled molecular machine, regulating an osmotic motor that tunes the thickness, spacing, and refractive index of the tunable, membrane-bound Bragg lamellae in the iridocytes of the loliginid squids. The tunable reflectin proteins, characterized by a variable number of highly conserved peptide domains interspersed with positively charged linker segments, are restricted in intra- and inter-chain contacts by Coulombic repulsion. Physiologically, this inhibition is progressively overcome by charge-neutralization resulting from acetylcholine (neurotransmitter)-induced, site-specific phosphorylation, triggering the simultaneous activation and progressive tuning of reflectance from red to blue. Details of this process have been resolved through in vitro analyses of purified recombinant reflectins, controlling charge-neutralization by pH-titration or mutation as surrogates for the in vivo phosphorylation. Results of these analyses have shown that neutralization overcoming the Coulombic inhibition reversibly and cyclably triggers condensation and secondary folding of the reflectins, with the emergence of previously cryptic, phase-segregated hydrophobic domains enabling hierarchical assembly. This tunable, reversible, and cyclable assembly regulates the Gibbs-Donnan mediated osmotic shrinking or swelling of the Bragg lamellae that tunes the brightness and color of reflected light. Our most recent studies have revealed a direct relationship between the extent of charge neutralization and the size of the reflectin assemblies, further explaining the synergistic effects on the intensity and wavelength of reflected light. Mutational analyses show that the “switch” controlling reflectins’ structural transitions is distributed along the protein, while detailed comparisons of the sequences and structures of the recently evolved tunable reflectins to those of their ancestral, non-tunable homologs are helping to identify the specific structural determinants governing tunability.},
doi = {10.1063/1.4985758},
journal = {APL Materials},
number = 10,
volume = 5,
place = {United States},
year = {2017},
month = {8}
}

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