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This article is published as part of a themed issue of
Photochemical & Photobiological Sciences on
Photofunctional proteins: from understanding to engineering
Guest edited by Aba Losi, Cristiano Viappiani and Santi Nonell
Downloaded on 08 October 2010
Published on 17 September 2010 on http://pubs.rsc.org | doi:10.1039/C005529H
Published in issue 10, 2010
Perspectives
Engineered photoreceptors as novel optogenetic tools
A. Möglich and K. Moffat, Photochem. Photobiol. Sci., 2010, 9, 1286, DOI: 10.1039/C0PP00167H
Fluorescent proteins as light-inducible photochemical partners
K. A. Lukyanov, E. O. Serebrovskaya, S. Lukyanov and D. M. Chudakov, Photochem. Photobiol. Sci., 2010,
9, 1301, DOI: 10.1039/C0PP00114G
Photoswitching of E222Q GFP mutants: “concerted” mechanism of chromophore
isomerization and protonation
S. Abbruzzetti, R. Bizzarri, S. Luin, R. Nifosì, B. Storti, C. Viappiani and F. Beltram, Photochem. Photobiol.
Sci., 2010, 9, 1307, DOI: 10.1039/C0PP00189A
Papers
A photoswitchable DNA-binding protein based on a truncated GCN4-photoactive yellow
protein chimera
S.-A. Morgan and G. A. Woolley, Photochem. Photobiol. Sci., 2010, 9, 1320, DOI: 10.1039/C0PP00214C
Differentiation of photocycle characteristics of flavin-binding BLUF domains of α- and βsubunits of photoactivated adenylyl cyclase of Euglena gracilis
S. Ito, A. Murakami, M. Iseki, T. Takahashi, S. Higashi and M. Watanabe, Photochem. Photobiol. Sci., 2010,
9, 1327, DOI: 10.1039/C0PP00130A
Diffusion pathways of oxygen species in the phototoxic fluorescent protein KillerRed
A. Roy, P. Carpentier, D. Bourgeois and M. Field, Photochem. Photobiol. Sci., 2010, 9, 1336, DOI:
10.1039/C0PP00141D
Singlet oxygen photosensitisation by GFP mutants: oxygen accessibility to the
chromophore
A. Jiménez-Banzo, X. Ragàs, S. Abbruzzetti, C. Viappiani, B. Campanini, C. Flors and S. Nonell,
Photochem. Photobiol. Sci., 2010, 9, 1342, DOI: 10.1039/C0PP00125B
EDITORIAL
www.rsc.org/pps | Photochemical & Photobiological Sciences
Photofunctional proteins: from understanding to
engineering
Downloaded on 08 October 2010
Published on 17 September 2010 on http://pubs.rsc.org | doi:10.1039/C005529H
DOI: 10.1039/c005529h
Photofunctional proteins, i.e. proteins that
elicit or change a physiological function
in response to light absorption, have
long been recognized as underpinning a
plethora of biological functions ranging
from vision to plant growth, light sensing
and DNA repair. Over the years, a wealth
of information has been gained on the
structure and function of these proteins.
The field has grown mature enough for
researchers to begin exploring the applications of this valuable knowledge. The ability to both engineer proteins to suit particular demands and also to express them
selectively in a particular cell organelle
holds the very appealing potential of being
able to genetically encode a light-inducible
biological function and thus control it with
an unprecedented degree of selectivity. It is
unquestionable now that the development
of fluorescent proteins has revolutionized
the field of molecular biology and in fact
this was recognized with the 2008 Nobel
Prize awarded to the pioneers in the field
Osamu Shimomura, Martin Chalfie and
Roger Y. Tsien. The time has come for
the field to evolve from using proteins as
sensors to applying them as actuators to
control a biological function. This themed
issue of Photochemical & Photobiological Sciences presents our readers with
a number of contributions that superbly
exemplify this emerging concept.
The first group of papers is devoted to
the exciting field of optogenetics, where
light-gated proteins originally designed by
nature, also known as photoreceptors,
are exploited as tools to elegantly photomodulate cell activities. In contrast to
fluorescent reporters, light-gated proteins
are supposed to perturb processes in optogenetics studies, and do so with exquisite
spatiotemporal control, in many cases by
means of chimeric proteins. The perspective paper from Möglich and Moffat reviews the state-of-the art and also offers an
excellent starting point for beginners with
the desire to enter the field. The focus is
on engineering strategies – from mutation
to truncations – to optimize the dynamic
range of application of light-gated proteins, the allosteric control of protein activities and their applicability to solving peculiar cell or even physiological “problems”.
The main characters of the plot depicted
by Möglich and Moffat are blue-light
sensors of the LOV family and the redlight responding phytochromes, but other
successful examples are discussed, chiefly
the famous protein channelrhodopsin. An
example of optimized optogenetics is given
by Morgan and Woolley, which can now
distinguish, by suitable truncations and
mutations, whether a DNA-binding protein fused to photoactive yellow protein
increases or decreases its DNA affinity
upon light activation. Crucial aspects of
naturally-occurring and engineered lightgated proteins are the quantum yield and
dynamics of their photocycle. Ito et al.
demonstrate that, in a photoswitchable
adenylate cyclase, they can be modulated
by introducing mutations within the bluelight sensing BLUF domain, an idea suggested to the authors by a naturally occurring variation in the BLUF family.
The second group of papers is devoted
to fluorescent proteins. They have been
long used as genetically encoded markers
and sensors. The emerging trend is to
This journal is © The Royal Society of Chemistry and Owner Societies 2010
develop them into photosensitisers, which
might prove useful in, e.g. chromophoreassisted light inactivation (CALI), a wellestablished tool in structural biology, or
for photodynamic therapy applications.
The perspective by Lukyanov et al. offers an excellent introduction to the field
and provides a privileged insight into
the foreseeable trends in the future. Roy
et al. in turn show in their very elegant studies the usefulness of molecular dynamics simulations to ascertain the
diffusion pathways of dioxygen and the
superoxide radical anion within the protein. This topic is examined also using an
experimental approach by Jiménez-Banzo
et al., who study the production of singlet
oxygen by a number of green fluorescent protein mutants with variable degrees
of oxygen accessibility to the protein’s
chromophore.
The third perspective in the themed
issue is contributed by Abbruzzetti
et al., who review the current understanding of the mechanism of photoswitching
of green fluorescent protein mutants. This
perspective will be most useful to those
readers interested in using fluorescent proteins for bioimaging applications, e.g. as
markers for high-resolution fluorescence
microscopy techniques.
We are grateful to all authors for
their excellent contributions and we
hope you find this issue on photofunctional proteins an enjoyable and valuable
read.
Aba Losi, Cristiano Viappiani and
Santi Nonell
Guest editors
Photochem. Photobiol. Sci., 2010, 9, 1285 | 1285