Source: ARIZONA STATE UNIVERSITY submitted to
ENERGY COUPLING IN THE PHOTOSYSTEM I SUPERCOMPLEXES
 
PROJECT DIRECTOR: Melkozernov, A. N. Blankenship, R. E.
 
PERFORMING ORGANIZATION
(N/A)
ARIZONA STATE UNIVERSITY
TEMPE,AZ 85287
 
NON TECHNICAL SUMMARY: Photosystem I (PSI) machinery consists of two parts, the core chlorophyll-a (Chl) reaction center complex, and the peripheral antenna, which function is accessory light-harvesting and possible energy flow regulation and photoprotection. The peripheral antennas are of different biochemical origin and structure. The peripheral antenna is structurally coupled to the PSI core, however, mechanisms of the energy coupling are unknown. They are thought to be associated with regulatory changes in the antenna in response to environmental conditions. The project studies molecular mechanisms of energy transfer between the light-harvesting antennas and the PSI core reaction center. Experiments help to find out differences in energy transfer flows in PSI supercomplexes adapted to either low light conditions (in cyanobacteria) or excess of light (PSI-LHCI in higher plants and green algae). Proposed biochemical and molecular biology manipulations with the pigment-binding sites in the peripheral antenna from higher plants test the molecular organization of the pigments and energy transfer processes in a possible protective mechanism against the excess energy damage. The overall purpose of the study is to gain a detailed knowledge of the molecular mechanisms of energy transfer in the PSI and their relationship to energy regulation. The long-term goal of the project is better understanding of regulatory mechanisms of photoprotection, energy storage in Photosystem I and stress physiology, which are important for plant productivity.
 
OBJECTIVES: The overall goal of the project is to probe functional energy coupling of the photosystem I (PSI) core reaction center complex with the peripheral light-harvesting antenna of different biochemical origin. We want to test the hypothesis that the energy coupling of the peripheral antenna associated with the PSI core is influenced by the light-harvesting strategy acquired by the photosynthetic organism in response to changing environmental conditions. The first objective of the project includes investigation of energy transfer pathways in the iron-stress induced PSI supercomplexes in aquatic cyanobacteria including analysis of the energy transfer processes in isolated iron-stress proteins, energy delocalization in the outer CP43` ring and its coupling to the PSI core. The second objective is analysis of energy transfer pathways in a dynamic LHCI Chl a/b binding antenna that harvests solar energy and perhaps also regulates energy flowing to the PSI core in response to illumination in the PSI supercomplexes from the green alga Chlamydomonas reinhardtii grown under State 1 - State 2 regulatory conditions. The third objective of the project includes time-resolved spectroscopy and biochemical study of pigment-pigment and pigment-protein interactions in the LHCI peripheral antenna from higher plants using recombinant Lhca1 and Lhca4 as a model.
 
APPROACH: Energy coupling in the photosystem I supercomplexes will be studied using modern ultrafast spectroscopy techniques including femtosecond transient absorption spectroscopy, fluorescence upconversion technique as well as picosecond fluorescence spectroscopy. Experiments will be performed with isolated PSI supercomplexes from iron-stress induced cyanobacteria and PSI-LHCI complexes from the green alga Chlamydomonas reinhardtii grown under State 1 - State 2 regulatory conditions. Isolated antenna proteins as well as PSI core complexes without peripheral antennas attached will be used as controls. Reconstituted and native proteins from tomato that form the LHCI peripheral antenna in higher plants will be used to elucidate details of energy transfer within the peripheral antenna. The apoproteins of Lhca1 and Lhca4 will be reconstituted with native chlorophylls a and b and carotenoids as well as with chlorophyll d and zeaxanthine in order to probe changed pigment occupancy in the complexes. The pigments will be purified by HPLC. The reconstituted His-tagged Lhca proteins will be isolated using FPLC and Ni-affinity chromatography. Site-directed mutations of pigment-binding sites in Lhca4 will be used for molecular identification of the Chl species participating in the red pigment's optical transition.
 
CRIS NUMBER: 0196258 SUBFILE: CRIS
PROJECT NUMBER: ARZR-2003-02413 SPONSOR AGENCY: NIFA
PROJECT TYPE: NRI COMPETITIVE GRANT PROJECT STATUS: EXTENDED MULTI-STATE PROJECT NUMBER: (N/A)
START DATE: Sep 1, 2003 TERMINATION DATE: Aug 31, 2007

GRANT PROGRAM: AGRICULTURAL PLANT BIOCHEMISTRY
GRANT PROGRAM AREA: Plant Systems

CLASSIFICATION
Knowledge Area (KA)Subject (S)Science (F)Objective (G)Percent
206249910002.280%
206249910402.220%

CLASSIFICATION HEADINGS
KA206 - Basic Plant Biology
S2499 - Plant research, general
F1000 - Biochemistry and biophysics
F1040 - Molecular biology
G2.2 - Increase Efficiency of Production and Marketing Systems


RESEARCH EFFORT CATEGORIES
BASIC 100%
APPLIED (N/A)%
DEVELOPMENTAL (N/A)%

KEYWORDS: photosynthesis; photosystem i; energy transfer; arizona; cyano bacteria; algae; coupling; energy metabolism; iron; transition; pigments; complexes; molecular biology; plant biology; plant biochemistry; reaction centers; light; metabolic pathways; environmental stress; plant ion stress; metabolic regulation; solar energy; chlamydomonas reinhardtii; chlorophylls; carotenoids; recombinant proteins; protein binding; binding sites; mechanism of action

PROGRESS: Oct 1, 2005 TO Sep 30, 2006
The work during this reporting period has been focused on the objective of the project dealing with analysis of structure-functional relationships in the peripheral antenna of low light adapted iron stress induced cyanobacteria by time-resolved spectroscopy. We wanted to answer the question whether structural integrity of the CP43` ring around the PSI trimer is important for maintaining the strong energy coupling in the supercomplex. In collaboration with J. Barber we tested energy transfer processes in the PSI-CP43` supercomplexes based on either PSI trimers or PSI monomers. Presence of the latter complexes was shown in PsaL-minus mutant iron-stress induced cells of Synechocystis sp. PCC 6803, where the supercomplex assembles as the PSI core monomers associated with 6 or 7 CP43` subunits attached to the PSI monomer. The overall architecture of these complexes bears resemblance with the modular structure of eukaryotic PSI-LHCI, for which we have detected presence of energy transfer processes in the peripheral antenna that are slower than the photochemical trapping in PSI core. Both absorption and fluorescence spectroscopy data showed that the excitation dynamics of the CP43`-PSI monomer based supercomplex is similar to those detected earlier for CP43`-PSI trimer based supercomplex. The data indicate that the PSI monomer based complex maintains the strong energy coupling. This is different from the PSI-LHCI monomer from eukaryotes. Analysis of the multiexponential fluorescence decay in the PSI-LHCI and its structural constituents, such as Lhca subunits, LHCI-730 dimer, bulk LHCI and the PSI core, suggest that the LHCI peripheral antenna, specific three-helical structure binding Chl a, Chl b and carotenoids, is responsible for the lengthening of the overall excitation decay in the eukaryotic PSI-LHCI.

IMPACT: 2005-10-01 TO 2006-09-30 The data provide insights into differences in energy transfer processes in PSI supercomplexes with similar reaction center core parts but structurally different peripheral antennas. This knowledge might be important for understanding the mechanisms of regulation of photosynthetic energy transfer.

PUBLICATION INFORMATION: 2005-10-01 TO 2006-09-30
No publications reported this period

PROJECT CONTACT INFORMATION
NAME: Melkozernov, A. N.
PHONE: 480-965-1437
FAX: 480-965-2747