Crystal structure of spinach major light-harvesting complex at 2.72 Å resolution

Abstract

The major light-harvesting complex of photosystem II (LHC-II) serves as the principal solar energy collector in the photosynthesis of green plants and presumably also functions in photoprotection under high-light conditions. Here we report the first X-ray structure of LHC-II in icosahedral proteoliposome assembly at atomic detail. One asymmetric unit of a large R32 unit cell contains ten LHC-II monomers. The 14 chlorophylls (Chl) in each monomer can be unambiguously distinguished as eight Chla and six Chlb molecules. Assignment of the orientation of the transition dipole moment of each chlorophyll has been achieved. All Chlb are located around the interface between adjacent monomers, and together with Chla they are the basis for efficient light harvesting. Four carotenoid-binding sites per monomer have been observed. The xanthophyll-cycle carotenoid at the monomer-monomer interface may be involved in the non-radiative dissipation of excessive energy, one of the photoprotective strategies that have evolved in plants.

A comparison of the three isoforms of the light-harvesting complex II using transient absorption and time-resolved fluorescence measurements

“…However, Caffarri et al did not report significant differences in the Chl b content of the three isoforms. In addition, there is also some discrepancy in the reported Chl a/b ratio for the three reconstituted isoforms, which is closer to the value of 1.33 observed in the new crystal structures of LHC II (Liu et al 2004;Standfuss et al 2005) in the samples prepared by Caffarri et al The protein residues which are needed for trimerization of LHC II complexes (Hobe et al 1995) are conserved in all the isoforms, but in contrast to Lhcb1 and Lhcb2, Lhcb3 alone does not form stable homotrimers in vitro (Standfuss and Ku¨hlbrandt 2004;Caffarri et al 2004). Furthermore, the N terminus of Lhcb3 is 10 residues shorter and lacks the phosphorylation site.…”

“…The 'blue' Chl b PB/SE disappears more rapidly than the signal of the 'red' Chls b, reflecting intraband equilibration within a pair of Chl b molecules due to strong coupling of Chl b molecules (Novoderezhjin et al 2004). In view of the new crystal structures (Liu et al 2004;Standfuss et al 2005), this may only occur between the Chls 10 and 13, which form the pair of Chls b that exhibit the strongest coupling strength. The lowest energy state(s) absorbing at around 680 nm (Pieper et al 1999) become(s) populated during the first few hundreds of fs.…”

“…Despite the good description of the absorbance, linear dichroism (LD), fluorescence and TA experiments, it should be realized that most of the experimental data were modeled with the atomic model at 3.4 Å resolution obtained by Ku¨hlbrandt et al (1994). However, very recently new atomic models for LHC II were obtained at 2.72 Å resolution by Liu et al (2004) and at 2.5 Å by Standfuss et al (2005) and many of the spectroscopic properties could be satisfactorily modeled (Novoderezhkin et al 2005). The new model shows two additional chlorophylls and furthermore, the identity and orientation of all the chlorophylls (8 Chls a and 6 Chls b) were revealed.…”

The xanthophyll cycle pool size controls the kinetics of non‐photochemical quenching in Arabidopsis thaliana

“…Xanthophyll cycle carotenoids are bound to the LHCII proteins [2][3][4][5], mostly at the peripheral V1 site [6,7]. There are two theories to explain the mechanism of action of these carotenoids in qE.…”

Special issue on Regulation of the Photosynthetic Systems in honor of Tingyun Kuang

“…In the subsequent time, her research team reported spectral and functional studies on siphonaxanthin-type light-harvesting complex of photosystem II from Bryopsis corticulan (Chen et al 2008;Wang et al 2013). In 2004, her team collaborated with the research group led by Professor Wenrui Chang and reported the crystal structure of spinach light-harvesting complex (LHCII) at 2.72 Å (Liu et al 2004). 5.…”