Developing a Structure–Function Model for the Cryptophyte Phycoerythrin 545 Using Ultrahigh Resolution Crystallography and Ultrafast Laser Spectroscopy

Doust, Alexander B.; Marai, Christopher N.J.; Harrop, S.J.; Wilk, Krystyna E.; Curmi, Paul M. G.; Scholes, Gregory D.

doi:10.1016/j.jmb.2004.09.044

Cited by 123 publications

(152 citation statements)

References 81 publications

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“…The structure of the PC645 dimer is very similar to the previously published closed structure of phycoerythrin PE545 from Rhodomonas CS24 (73% sequence identity; rmsd 0.85Å on 453 C α atoms) (3,4).…”

Section: Resultssupporting

confidence: 76%

“…The crystal structure of the cryptophyte PBP phycoerythrin PE545 from Rhodomonas CS24 showed that the protein is a dimer of two αβ monomers (3,4), the β subunit of which has a globin fold (5,6) and binds three linear tetrapyrroles (bilins), whereas the α subunit is a short, extended polypeptide with a single bilin chromophore. A prominent feature of this structure is the arrangement of the two central chromophores in van der Waals contact with each other on the pseudo-twofold axis, with each chromophore covalently linked to two cysteines on one of the β subunits (referred to as "β50/61").…”

mentioning

confidence: 99%

“…A prominent feature of this structure is the arrangement of the two central chromophores in van der Waals contact with each other on the pseudo-twofold axis, with each chromophore covalently linked to two cysteines on one of the β subunits (referred to as "β50/61"). This structural feature introduces excitonic coupling between the chromophores (3,4). We are fascinated by this observation because it implies that if coherence plays a nontrivial role in light harvesting (7)(8)(9)(10)(11)(12), it might be switched on and off (either dynamically or genetically) by controlling the separation, and hence excitonic coupling, between these two central chromophores.…”

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confidence: 99%

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Single-residue insertion switches the quaternary structure and exciton states of cryptophyte light-harvesting proteins

Harrop

Wilk

Dinshaw

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

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141

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Observation of coherent oscillations in the 2D electronic spectra (2D ES) of photosynthetic proteins has led researchers to ask whether nontrivial quantum phenomena are biologically significant. Coherent oscillations have been reported for the soluble light-harvesting phycobiliprotein (PBP) antenna isolated from cryptophyte algae. To probe the link between spectral properties and protein structure, we determined crystal structures of three PBP light-harvesting complexes isolated from different species. Each PBP is a dimer of αβ subunits in which the structure of the αβ monomer is conserved. However, we discovered two dramatically distinct quaternary conformations, one of which is specific to the genus Hemiselmis. Because of steric effects emerging from the insertion of a single amino acid, the two αβ monomers are rotated by ∼73°to an "open" configuration in contrast to the "closed" configuration of other cryptophyte PBPs. This structural change is significant for the light-harvesting function because it disrupts the strong excitonic coupling between two central chromophores in the closed form. The 2D ES show marked cross-peak oscillations assigned to electronic and vibrational coherences in the closedform PC645. However, such features appear to be reduced, or perhaps absent, in the open structures. Thus cryptophytes have evolved a structural switch controlled by an amino acid insertion to modulate excitonic interactions and therefore the mechanisms used for light harvesting.X-ray crystallography | quantum coherence | protein evolution | excitonic switching L ight-harvesting complexes capture and funnel the energy from light using organic chromophore molecules that are bound to scaffolding proteins. The protein structure thereby sets the relative positions and orientations of the chromophores to control excitation transport. In other words, the protein plays a deciding role in building the "electronic Hamiltonian"-the electronic coupling between chromophores and the chromophoric energy landscape that directs energy flow. This strong connection between structural biology and physics means that ultrafast light-harvesting functions are under genetic and evolutionary control. Cryptophytes, a group of marine and freshwater single-celled algae, are an intriguing example, because one of their light-harvesting antenna complexes was completely reengineered by combining a unique bilin-binding polypeptide with a single subunit from the ancestral red algal phycobilisome (1, 2). Here we report a further example of biological manipulation of this phycobiliprotein (PBP) light-harvesting system. We have discovered an elegant but powerful genetic switch that converts the common form of this PBP into a distinct structural form in which the mechanism underpinning light harvesting is vastly different-in essence because strong excitonic interactions within the PBP are switched from on to off.The crystal structure of the cryptophyte PBP phycoerythrin PE545 from Rhodomonas CS24 showed that the protein is a dimer of two αβ monomers (3, ...

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Section: Resultssupporting

confidence: 76%

mentioning

confidence: 99%

mentioning

confidence: 99%

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Single-residue insertion switches the quaternary structure and exciton states of cryptophyte light-harvesting proteins

Harrop

Wilk

Dinshaw

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

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141

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“…Moreover, the typical timescale associated with equilibration of the protein and solvent environment of chromophores in response to electronic excitation is often comparable with the timescale of excitation dynamics, adding a further challenging aspect for theory [57,62,63]. In addition, strong coupling to selective vibrations, for example of intramolecular origin, are commonplace in molecular systems [64][65][66]. This means that non-equilibrium vibrational dynamics can actively participate in energy transfer and are likely to be underlying, at least partly, the observation of long-lived coherent dynamics [57,67,68].…”

Section: Energy Transfer and The Question Of Coherencementioning

confidence: 99%

“…Otherwise, non-equilibrium phonon processes take place [62,63]. The second source of non-equilibrium phonon dynamics comes from discrete modes that strongly couple to the system [64][65][66][67][68][116][117][118]. One way of capturing such phonon dynamics is to explicitly include them as part of the system under study while the rest of the phonon modes can be treated as the (possibly in equilibrium) environment [116,118].…”

Section: Coherent Exciton Dynamics and Non-equilibrium Phononsmentioning

confidence: 99%

Photosynthetic light harvesting: excitons and coherence

Fassioli

Dinshaw

Arpin

et al. 2014

J. R. Soc. Interface.

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269

297

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Photosynthesis begins with light harvesting, where specialized pigmentprotein complexes transform sunlight into electronic excitations delivered to reaction centres to initiate charge separation. There is evidence that quantum coherence between electronic excited states plays a role in energy transfer. In this review, we discuss how quantum coherence manifests in photosynthetic light harvesting and its implications. We begin by examining the concept of an exciton, an excited electronic state delocalized over several spatially separated molecules, which is the most widely available signature of quantum coherence in light harvesting. We then discuss recent results concerning the possibility that quantum coherence between electronically excited states of donors and acceptors may give rise to a quantum coherent evolution of excitations, modifying the traditional incoherent picture of energy transfer. Key to this (partially) coherent energy transfer appears to be the structure of the environment, in particular the participation of non-equilibrium vibrational modes. We discuss the open questions and controversies regarding quantum coherent energy transfer and how these can be addressed using new experimental techniques.

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Structure of the Phycobilisome Antennae in Cyanobacteria and Red Algae

Adir¹

2008

Photosynthetic Protein Complexes

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Developing a Structure–Function Model for the Cryptophyte Phycoerythrin 545 Using Ultrahigh Resolution Crystallography and Ultrafast Laser Spectroscopy

Cited by 123 publications

References 81 publications

Single-residue insertion switches the quaternary structure and exciton states of cryptophyte light-harvesting proteins

Single-residue insertion switches the quaternary structure and exciton states of cryptophyte light-harvesting proteins

Photosynthetic light harvesting: excitons and coherence

Structure of the Phycobilisome Antennae in Cyanobacteria and Red Algae

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