title: S-state dependent Fourier transform infrared difference spectra for the photosystem II oxygen evolving complex.
abstract: Vibrational spectroscopy provides a means to investigate molecular interactions within the active site of an enzyme. We have applied difference FTIR spectroscopy coupled with a flash turnover protocol of photosystem II (PSII) to study the oxygen evolving complex (OEC). Our data show two overlapping oscillatory patterns as the sample is flashed through the four-step S-state cycle that produces O(2) from two H(2)O molecules. The first oscillation pattern of the spectra shows a four-flash period four oscillation and reveals a number of new vibrational modes for each S-state transition, indicative of unique structural changes involved in the formation of each S-state. Importantly, the first and second flash difference spectra are reproduced in the 1800-1200 cm(-)(1) spectral region by the fifth and sixth flash difference spectra, respectively. The second oscillation pattern observed is a four-flash, period-two oscillation associated with changes primarily to the amide I and II modes and reports on changes in sign of these modes that alternate 0:0:1:1 during S-state advance. This four-flash, period-two oscillation undergoes sign inversion that alternates during the S(1)-to-S(2) and S(3)-to-S(0) transitions. Underlying this four-flash period two is a small-scale change in protein secondary structure in the PSII complex that is directly related to S-state advance. These oscillation patterns and their relationships with other PSII phenomena are discussed, and future work can initiate more detailed vibrational FTIR studies for the S-state transitions providing spectral assignments and further structural and mechanistic insight into the photosynthetic water oxidation reaction.
authors.affiliation: Department of Chemistry, Michigan State University, East Lansing, MI 48824, USA.
authors.forename: W
authors.initials: W
authors.lastname: Hillier
authors.forename: G T
authors.initials: GT
authors.lastname: Babcock
mesh_terms: D000577:Amides / Q000737:chemistry; D002264:Carboxylic Acids / Q000737:chemistry; D003624:Darkness; D006860:Hydrogen Bonding; D007834:Lasers; D010100:Oxygen / Q000378:metabolism*; D010782:Photolysis; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry* / Q000378:metabolism; D045332:Photosystem II Protein Complex; D011487:Protein Conformation; D017550:Spectroscopy, Fourier Transform Infrared / Q000379:methods; D018724:Spinacia oleracea; D013696:Temperature
chemical_list: D000577:Amides; D002264:Carboxylic Acids; D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; D010100:Oxygen