Carotenoid-chlorophyll coupling and fluorescence quenching in aggregated minor PSII proteins CP24 and CP29.
It is known that aggregation of isolated light-harvesting complex II (LHCII) in solution results in high fluorescence quenching, reduced chlorophyll fluorescence lifetime, and increased electronic coupling of carotenoid (Car) S1 and chlorophyll (Chl) Qy states, as determined by two-photon studies. It has been suggested that this behavior of aggregated LHCII mimics aspects of non-photochemical quenching processes of higher plants and algae. However, several studies proposed that the minor photosystem II proteins CP24 and CP29 also play a significant role in regulation of photosynthesis. Therefore, we use a simple protocol that allows gradual aggregation also of CP24 and CP29. Similarly, as observed for LHCII, aggregation of CP24 and CP29 also leads to increasing fluorescence quenching and increasing electronic Car S1-Chl Qy coupling. Furthermore, a direct comparison of the three proteins revealed a significant higher electronic coupling in the two minor proteins already in the absence of any aggregation. These differences become even more prominent upon aggregation. A red-shift of the Qy absorption band known from LHCII aggregation was also observed for CP29 but not for CP24. We discuss possible implications of these results for the role of CP24 and CP29 as potential valves for excess excitation energy in the regulation of photosynthetic light harvesting.
Department for Biophysical Chemistry, Institute for Physical and Theoretical Chemistry, Technische Universität Braunschweig, Hans-Sommer-Str. 10, 38106, Braunschweig, Germany.
Christoph-Peter
CP
Holleboom
Daniel Alexander
DA
Gacek
Pen-Nan
PN
Liao
Marco
M
Negretti
Roberta
R
Croce
Peter Jomo
PJ
Walla
D002247:Carbon Isotopes / Q000032:analysis; D002338:Carotenoids / Q000737:chemistry / Q000378:metabolism*; D002734:Chlorophyll / Q000737:chemistry / Q000378:metabolism; D061146:Chlorophyll Binding Proteins / Q000737:chemistry / Q000378:metabolism*; D000460:Chlorophyta / Q000737:chemistry / Q000378:metabolism; D005453:Fluorescence; D045342:Light-Harvesting Protein Complexes / Q000737:chemistry / Q000378:metabolism*; D010788:Photosynthesis; D045332:Photosystem II Protein Complex / Q000737:chemistry / Q000378:metabolism*; D010940:Plant Proteins / Q000737:chemistry / Q000378:metabolism; D010944:Plants / Q000737:chemistry / Q000378:metabolism*; D000461:Rhodophyta / Q000737:chemistry / Q000378:metabolism
C069660:CP29 light harvesting complex; D002247:Carbon Isotopes; D061146:Chlorophyll Binding Proteins; D045342:Light-Harvesting Protein Complexes; D045332:Photosystem II Protein Complex; D010940:Plant Proteins; D002734:Chlorophyll; D002338:Carotenoids