Structure-function relationships in the 47-kDa antenna protein and its complex with the photosystem II reaction center core: insights from picosecond fluorescence decay kinetics and resonance Raman spectroscopy.
We report the fluorescence decay kinetics and the vibrational properties of chlorophyll a bound to the 47-kDa antenna protein (CP47) of spinach photosystem II. The chlorophyll fluorescence of CP47 samples decays with four lifetimes (tau = 75.8 ps, 1.05 ns, 3.22 ns, and 5.41 ns). The 75.8-ps and 3.22-ns components are associated with chlorophyll a bound to relatively intact centers, the 1.05-ns component corresponds to chlorophyll bound to centers that are slightly perturbed, and the the 5.41-ns phase probably originates from centers that are severely denatured. The resonance Raman spectrum of CP47 at 441.6 nm (this work) and at 406.7 nm [de Paula, J. C., Ghanotakis, D. F., Bowlby, N. R., Dekker, J. P., Yocum, C. F., & Babcock, G. T. (1990) in Current Research in Photosynthesis (Baltscheffsky, M., Ed.), Vol. I, pp 643-646, Kluwer Academic Publishers, Dordrecht, The Netherlands] shows heterogeneity in the C = O stretching region. This part of the spectrum monitors the environment of the keto group at position 9 of the chlorophyll a molecule. We show that several structurally distinct pools of chlorophyll a are bound to CP47. Four of these may be distinguished by their C9 = O stretching frequencies (nu C = O = 1670, 1688, 1693, and 1701 cm-1). By analyzing the resonance enhancement pattern of these modes, we ascribe the 1693-cm-1 vibration to denatured centers. Of the remaining populations, we propose that the 1670-cm-1 vibration is consistent with a hydrogen bond between the C9 = O group of chlorophyll a and the protein. We elaborate on the role of this chromophore-protein interaction in the mechanism of energy transfer within the 47-kDa antenna protein.
de Paula
J C
JC
Department of Chemistry, Haverford College, Pennsylvania 19041.
Liefshitz
A
A
Hinsley
S
S
Lin
W
W
Chopra
V
V
Long
K
K
Williams
S A
SA
Belts
S
S
Yocum
C F
CF
D002734:Chlorophyll / Q000378:metabolism; D000077194:Chlorophyll A; D005960:Glucosides; D006860:Hydrogen Bonding; D007700:Kinetics; D045342:Light-Harvesting Protein Complexes; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry* / Q000378:metabolism*; D045332:Photosystem II Protein Complex; D010944:Plants / Q000737:chemistry*; D012995:Solubility; D013050:Spectrometry, Fluorescence; D013059:Spectrum Analysis, Raman; D013329:Structure-Activity Relationship
D005960:Glucosides; D045342:Light-Harvesting Protein Complexes; D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; C070970:photosystem II, chlorophyll-binding protein, CP-47; D002734:Chlorophyll; C040358:dodecyl maltoside; D000077194:Chlorophyll A