Xanthophylls of the major photosynthetic light-harvesting complex of plants: identification, conformation and dynamics

The electronic transitions of lutein and neoxanthin in the major light-harv esting complex, LHCIIb, have been identified for the first time. It was fou nd that 0-0, 0-1 and 0-2 transitions of neoxanthin were located around 486, 457 and 430 nm, whilst those for lutein were dependent on the oligomerisat ion state. For the monomer, the absorption bands of lutein were found at 49 5, 466 and 437 nm, Trimerisation caused a decrease in lutein absorption and the parallel appearance of an additional absorption band around 510 nm, wh ich was identified by resonance Raman excitation spectra to originate from lutein, Circular dichroism measurements together with analysis of the nu(4) resonance Raman region of xanthophylls suggested that this lutein molecule is distorted in the trimer, This feature is not predicted by the LHCIIb at omic model of Kuhlbrandt and coworkers [Kuhlbrandt, W,, Wang, D.N. and Fugi yoshi, Y, (1994) Nature 367, 614-621] and is an important step in understan ding pigment dynamics of the complex. Oligomerisation of trimers led to a s pecific distortion of the neoxanthin molecule. These observations suggest t hat the xanthophylls of LHCIIb sense the protein conformation and which may reflect their special role in the assembly and function of the light-harve sting antenna of higher plants. (C) 2000 Federation of European Biochemical Societies. Published by Elsevier Science B.V. All rights reserved.