Pigment structure in the light-harvesting protein of the siphonous green alga Codium fragile.

Affiliation

Streckaite S(1), Llansola-Portoles MJ(1), Pascal AA(1), Ilioaia C(1), Gall A(1), Seki S(2), Fujii R(3), Robert B(4).
Author information:
(1)Université Paris-Saclay, CEA, CNRS, Institute for Integrative Biology of the Cell
(I2BC), 91198 Gif-sur-Yvette, France.
(2)Osaka City University, Graduate School of Science, Sumiyoshi Ku, 3-3-138 Sugimoto, Osaka 5588585, Japan.
(3)Osaka City University, Graduate School of Science, Sumiyoshi Ku, 3-3-138 Sugimoto, Osaka 5588585, Japan; Osaka City University, The OCU Research Center for Artificial Photosynthesis, Sumiyoshi Ku, 3-3-138 Sugimoto, Osaka 5588585, Japan.
(4)Université Paris-Saclay, CEA, CNRS, Institute for Integrative Biology of the Cell
(I2BC), 91198 Gif-sur-Yvette, France. Electronic address: [Email]

Abstract

The siphonaxanthin-siphonein-chlorophyll-a/b-binding protein (SCP), a trimeric light-harvesting complex isolated from photosystem II of the siphonous green alga Codium fragile, binds the carotenoid siphonaxanthin (Sx) and/or its ester siphonein in place of lutein, in addition to chlorophylls a/b and neoxanthin. SCP exhibits a higher content of chlorophyll b (Chl-b) than its counterpart in green plants, light-harvesting complex II (LHCII), increasing the relative absorption of blue-green light for photosynthesis. Using low temperature absorption and resonance Raman spectroscopies, we reveal the presence of two non-equivalent Sx molecules in SCP, and assign their absorption peaks at 501 and 535 nm. The red-absorbing Sx population exhibits a significant distortion that is reminiscent of lutein 2 in trimeric LHCII. Unexpected enhancement of the Raman modes of Chls-b in SCP allows an unequivocal description of seven to nine non-equivalent Chls-b, and six distinct Chl-a populations in this protein.