Molecular mechanism of reflectin’s tunable biophotonic control: Opportunities and limitations for new optoelectronics
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...
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doaj-594a00d7d16544718c97de231be0b1782020-11-25T00:41:47ZengAIP Publishing LLCAPL Materials2166-532X2017-10-01510104801104801-1210.1063/1.4985758001795APMMolecular mechanism of reflectin’s tunable biophotonic control: Opportunities and limitations for new optoelectronicsRobert Levenson0Daniel G. DeMartini1Daniel E. Morse2Department of Molecular, Cellular and Developmental Biology and the Institute for Collaborative Biotechnologies, University of California, Santa Barbara, California 93106-5100, USADepartment of Molecular, Cellular and Developmental Biology and the Institute for Collaborative Biotechnologies, University of California, Santa Barbara, California 93106-5100, USADepartment of Molecular, Cellular and Developmental Biology and the Institute for Collaborative Biotechnologies, University of California, Santa Barbara, California 93106-5100, USADiscovery 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.http://dx.doi.org/10.1063/1.4985758 |
collection |
DOAJ |
language |
English |
format |
Article |
sources |
DOAJ |
author |
Robert Levenson Daniel G. DeMartini Daniel E. Morse |
spellingShingle |
Robert Levenson Daniel G. DeMartini Daniel E. Morse Molecular mechanism of reflectin’s tunable biophotonic control: Opportunities and limitations for new optoelectronics APL Materials |
author_facet |
Robert Levenson Daniel G. DeMartini Daniel E. Morse |
author_sort |
Robert Levenson |
title |
Molecular mechanism of reflectin’s tunable biophotonic control: Opportunities and limitations for new optoelectronics |
title_short |
Molecular mechanism of reflectin’s tunable biophotonic control: Opportunities and limitations for new optoelectronics |
title_full |
Molecular mechanism of reflectin’s tunable biophotonic control: Opportunities and limitations for new optoelectronics |
title_fullStr |
Molecular mechanism of reflectin’s tunable biophotonic control: Opportunities and limitations for new optoelectronics |
title_full_unstemmed |
Molecular mechanism of reflectin’s tunable biophotonic control: Opportunities and limitations for new optoelectronics |
title_sort |
molecular mechanism of reflectin’s tunable biophotonic control: opportunities and limitations for new optoelectronics |
publisher |
AIP Publishing LLC |
series |
APL Materials |
issn |
2166-532X |
publishDate |
2017-10-01 |
description |
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. |
url |
http://dx.doi.org/10.1063/1.4985758 |
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