title: Conformational switching explains the intrinsic multifunctionality of plant light-harvesting complexes.
abstract: The light-harvesting complexes of photosystem I and II (Lhcas and Lhcbs) of plants display a high structural homology and similar pigment content and organization. Yet, the spectroscopic properties of these complexes, and accordingly their functionality, differ substantially. This difference is primarily due to the charge-transfer (CT) character of a chlorophyll dimer in all Lhcas, which mixes with the excitonic states of these complexes, whereas this CT character is generally absent in Lhcbs. By means of single-molecule spectroscopy near room temperature, we demonstrate that the presence or absence of such a CT state in Lhcas and Lhcbs can occasionally be reversed; i.e., these complexes are able to interconvert conformationally to quasi-stable spectral states that resemble the Lhcs of the other photosystem. The high structural similarity of all the Lhca and Lhcb proteins suggests that the stable conformational states that give rise to the mixed CT-excitonic state are similar for all these proteins, and similarly for the conformations that involve no CT state. This indicates that the specific functions related to Lhca and Lhcb complexes are realized by different stable conformations of a single generic protein structure. We propose that this functionality is modulated and controlled by the protein environment.
authors.affiliation: Department of Physics and Astronomy, Faculty of Sciences, Vrije Universiteit, De Boelelaan 1081, 1081 HV Amsterdam, The Netherlands.
authors.forename: Tjaart P J
authors.initials: TP
authors.lastname: Krüger
authors.forename: Emilie
authors.initials: E
authors.lastname: Wientjes
authors.forename: Roberta
authors.initials: R
authors.lastname: Croce
authors.forename: Rienk
authors.initials: R
authors.lastname: van Grondelle
mesh_terms: D017360:Arabidopsis / Q000737:chemistry / Q000502:physiology; D002734:Chlorophyll / Q000737:chemistry*; D019281:Dimerization; D004735:Energy Transfer; D045342:Light-Harvesting Protein Complexes / Q000737:chemistry*; D045331:Photosystem I Protein Complex / Q000737:chemistry; D045332:Photosystem II Protein Complex / Q000737:chemistry; D010940:Plant Proteins; D011487:Protein Conformation; D013057:Spectrum Analysis
chemical_list: D045342:Light-Harvesting Protein Complexes; D045331:Photosystem I Protein Complex; D045332:Photosystem II Protein Complex; D010940:Plant Proteins; D002734:Chlorophyll