Spectral substructure and excitonic interactions in the minor photosystem II antenna complex CP29 as revealed by nonlinear polarization spectroscopy in the frequency domain.
CP29 (the lhcb4 gene product), a minor photosystem II antenna complex, binds six chlorophyll (Chl) a, two Chl b, and two to three xanthophyll molecules. The Chl a/b Q(y) absorption band substructure of CP29 (purified from spinach) was investigated by nonlinear polarization spectroscopy in the frequency domain (NLPF) at room temperature. A set of NLPF spectra was obtained at 11 probe wavelengths. Seven probe wavelengths were located in the Q(y) spectral region (between 630 and 690 nm) and four in the Soret band (between 450 and 485 nm). Evaluation of the experimental data within the framework of global analysis leads to the following conclusions: (i) The dominant Chl a absorption (with a maximum at 674 nm) splits into (at least) three subbands (centered at 660, 670, and 681.5 nm). (ii) In the Chl b region two subbands can be identified with maxima located at 640 and 646 nm. (iii) The lowest energy Q(y) transition (peaking at 681.5 nm) is assigned to a Chl a which only weakly interacts with other Chl aor b molecules by incoherent Förster-type excitation energy transfer. (iv) Pronounced excitonic interaction exists between certain Chl a and Chl b molecules, which most likely form a Chl a/b heterodimer. The subbands centered at 640 and 670 nm constitute a strongly coupled Chl a/b pair. The findings of the study indicate that the currently favored view of spectral heterogeneity in CP29 being due essentially to pigment-protein interactions has to be revised.
Voigt
Bernd
B
Max-Born-Institut für Nichtlineare Optik und Kurzzeitspektroskopie, Max-Born-Strasse 2a, D-12489 Berlin, Germany. voigy@mbi-berlin.de
Irrgang
Klaus-Dieter
KD
Ehlert
Jürgen
J
Beenken
Wichard
W
Renger
Gernot
G
Leupold
Dieter
D
Lokstein
Heiko
H
D002734:Chlorophyll / Q000737:chemistry; D000077194:Chlorophyll A; D045342:Light-Harvesting Protein Complexes; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry*; D045332:Photosystem II Protein Complex; D010940:Plant Proteins / Q000737:chemistry*; D017434:Protein Structure, Tertiary; D013054:Spectrophotometry, Atomic; D018724:Spinacia oleracea / Q000737:chemistry*
C069660:CP29 light harvesting complex; D045342:Light-Harvesting Protein Complexes; D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; D010940:Plant Proteins; D002734:Chlorophyll; C037184:chlorophyll b; D000077194:Chlorophyll A