title: Light-induced dynamics in photosystem I electron transfer.
abstract: Protein dynamics are likely to play important, regulatory roles in many aspects of photosynthetic electron transfer, but a detailed description of these coupled protein conformational changes has been unavailable. In oxygenic photosynthesis, photosystem I catalyzes the light-driven oxidation of plastocyanin or cytochrome c and the reduction of ferredoxin. A chlorophyll (chl) a/a' heterodimer, P(700), is the secondary electron donor, and the two P(700) chl, are designated P(A) and P(B). We used specific chl isotopic labeling and reaction-induced Fourier-transform infrared spectroscopy to assign chl keto vibrational bands to P(A) and P(B). In the cyanobacterium, Synechocystis sp. PCC 6803, the chl keto carbon was labeled from (13)C-labeled glutamate, and the chl keto oxygen was labeled from (18)O(2). These isotope-based assignments provide new information concerning the structure of P(A)(+), which is found to give rise to two chl keto vibrational bands, with frequencies at 1653 and 1687 cm(-1). In contrast, P(A) gives rise to one chl keto band at 1638 cm(-1). The observation of two P(A)(+) keto frequencies is consistent with a protein relaxation-induced distribution in P(A)(+) hydrogen bonding. These results suggest a light-induced conformational change in photosystem I, which may regulate the oxidation of soluble electron donors and other electron-transfer reactions. This study provides unique information concerning the role of protein dynamics in oxygenic photosynthesis.
authors.affiliation: School of Chemistry and Biochemistry, Georgia Institute of Technology and the Petit Institute of Bioengineering and Bioscience, Atlanta, Georgia 30332, USA.
authors.forename: Shana L
authors.initials: SL
authors.lastname: Bender
authors.forename: Bridgette A
authors.initials: BA
authors.lastname: Barry
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism; D002734:Chlorophyll / Q000737:chemistry; D000077194:Chlorophyll A; D004579:Electron Transport / Q000528:radiation effects; D008027:Light; D045331:Photosystem I Protein Complex / Q000737:chemistry / Q000378:metabolism*; D017433:Protein Structure, Secondary; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D017550:Spectroscopy, Fourier Transform Infrared; D046939:Synechocystis / Q000378:metabolism* / Q000528:radiation effects*
chemical_list: D001426:Bacterial Proteins; D045331:Photosystem I Protein Complex; D002734:Chlorophyll; D000077194:Chlorophyll A