Identification of Carotenoids in Photosynthetic Proteins: Xanthophylls of the Light Harvesting Antenna - Carotenoids: Physical, Chemical, and Biological Functions and Properties - page 121

Taking into consideration that antenna xanthophylls not only possess original absorption but
also resonance Raman spectra, and the fact that the Raman signal is virtually free from vibrational
spectroscopy artifacts (water, sample condition, etc.), it seemed of obvious advantage to apply the
described combination of spectroscopies for the identii cation of these pigments.

7.5 IDENTIFICATION OF XANTHOPHYLLS ASSOCIATED WITH THE
TRANSMEMBRANE HELIXES OF LHCII ANTENNA COMPLEX:
NEOXANTHIN AND LUTEIN
Neoxanthin and the two lutein molecules have close associations with three transmembrane helixes,
A, B, and C, forming three chlorophyll-xanthophyll-protein domains (Figure 7.5). Considering
the structure of LHCII complex in terms of domains is useful for understanding how the antenna
system works, and the functions of the different xanthophylls. Biochemical evidence suggests that
these xanthophylls have a much stronger afi nity of binding to LHCII in comparison to violaxanthin

Neoxanthin domain Lutein 1 domain

A-helix

C-helix

Neo

a610

b609

a611

b608

a612

b605

b606

b607

Lut1

B-helix

a604

Y

D-helix

Lutein 2 domain Violaxanthin domain

a602

b601

B-helix

A-helix

Vio

a603

Lut2

a613

a604

A-helix a614

W

F

D-helix

E-helix

FIGURE 7.5 Structural domains of LHCII xanthophylls. Aromatic amino acids tyrosine in the neoxanthin
domain and tryptophan and phenylalanine in the violaxanthin domain are labeled as Y, W, and F, respectively.