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Magneto-Optic Spectroscopy of a Protein Tetramer Binding Two Exciton-Coupled Chlorophylls

Hughes, Joseph; Razeghifard, Mohammad; Logue, Mark; Oakley, Aaron; Wydrzynski, Thomas; Krausz, Elmars

Description

In vitro chlorophyll (Chl) aggregates have often served as models for in vivo forms of long-wavelength Chl. However, the interaction of protein-bound Chl molecules is typically different than that occurring in solvent-based self-aggregates. We have chosen a water-soluble Chl-binding protein (WSCP) from cauliflower in order to help characterize the spectroscopic properties of Chl in a single well-defined native environment and also to study the pigment-pigment (exciton) interactions present in...[Show more]

dc.contributor.authorHughes, Joseph
dc.contributor.authorRazeghifard, Mohammad
dc.contributor.authorLogue, Mark
dc.contributor.authorOakley, Aaron
dc.contributor.authorWydrzynski, Thomas
dc.contributor.authorKrausz, Elmars
dc.date.accessioned2015-12-13T23:02:13Z
dc.identifier.issn0002-7863
dc.identifier.urihttp://hdl.handle.net/1885/84788
dc.description.abstractIn vitro chlorophyll (Chl) aggregates have often served as models for in vivo forms of long-wavelength Chl. However, the interaction of protein-bound Chl molecules is typically different than that occurring in solvent-based self-aggregates. We have chosen a water-soluble Chl-binding protein (WSCP) from cauliflower in order to help characterize the spectroscopic properties of Chl in a single well-defined native environment and also to study the pigment-pigment (exciton) interactions present in assemblies of this protein. WSCP forms tetrameric units upon binding two Chl molecules. We present the absorption, circular diohroism (CD), magnetic circular dichroism (MCD), and emission spectra at 1.7 K of recombinant WSCP tetramers containing either Chl a or Chl d. The spectroscopic characteristics provide evidence for significant exciton interaction between equivalent Chl molecules. Our simple exciton analysis allows an estimate of the molecular geometry of the dimer, which is predicted to have an "open sandwich"-type structure. We find that the ratio of the magnetic circular dichroism to absorption, ΔA/A, is substantially increased (∼60%) for Chl a in this system compared to its value in solution. This increase is in marked contrast to substantial reductions (>50%) of ΔA/A seen in solvent-based Chl aggregates and in photosynthetic reaction centers. Current theoretical models are unable to account for such large variations in the MCD to absorption ratio for Chl. We propose that spectroscopic studies of WSCP mutants will enable a fundamental understanding of Chl-Chl and Chl-protein interactions.
dc.publisherAmerican Chemical Society
dc.sourceJournal of the American Chemical Society
dc.subjectKeywords: Absorption; Aggregates; Chlorophyll; Excitons; Magnetooptical effects; Mathematical models; Molecular dynamics; Pigments; Circular diohroism (CD); Magnetic circular dichroism (MCD); Magneto-optic spectroscopy; Pigment-pigment (exciton) interactions; Water
dc.titleMagneto-Optic Spectroscopy of a Protein Tetramer Binding Two Exciton-Coupled Chlorophylls
dc.typeJournal article
local.description.notesImported from ARIES
local.description.refereedYes
local.identifier.citationvolume128
dc.date.issued2006
local.identifier.absfor030606 - Structural Chemistry and Spectroscopy
local.identifier.absfor060107 - Enzymes
local.identifier.ariespublicationMigratedxPub13033
local.type.statusPublished Version
local.contributor.affiliationHughes, Joseph, College of Physical and Mathematical Sciences, ANU
local.contributor.affiliationRazeghifard, Mohammad, College of Medicine, Biology and Environment, ANU
local.contributor.affiliationLogue, Mark, College of Medicine, Biology and Environment, ANU
local.contributor.affiliationOakley, Aaron, College of Physical and Mathematical Sciences, ANU
local.contributor.affiliationWydrzynski, Thomas, College of Medicine, Biology and Environment, ANU
local.contributor.affiliationKrausz, Elmars, College of Physical and Mathematical Sciences, ANU
local.description.embargo2037-12-31
local.bibliographicCitation.issue11
local.bibliographicCitation.startpage3649
local.bibliographicCitation.lastpage3658
local.identifier.doi10.1021/ja056576b
dc.date.updated2015-12-12T07:45:42Z
local.identifier.scopusID2-s2.0-33645406752
CollectionsANU Research Publications

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