A new function for the xanthophyll zeaxanthin: glueing chlorophyll biosynthesis to thylakoid protein assembly.

Roberto Bassi

doi:10.1042/bcj20200803

Abstract

Xanthophylls are coloured isoprenoid metabolites synthesized in many organisms with a variety of functions from the attraction of animals for impollination to absorption of light energy for photosynthesis to photoprotection against photooxidative stress. The finding by Proctor and co-workers makes a new addition to the last type of functions by showing that zeaxanthin is instrumental in coordinating chlorophyll biosynthesis with the insertion of pigment-binding proteins into the photosynthetic membrane by glueing the protein components catalyzing these functions into a supercomplex and regulating its activity.

Highlights

Commentary on: Xanthophyll carotenoids stabilise the association of cyanobacterial chlorophyll synthase with the light-harvesting complex (LHC)-like protein HliD
Chlorophylls, essential components for both light harvesting and charge separation reactions in all photosynthetic systems, have a major problem with oxygen: their triplet states react with O2 to yield singlet oxygen, a reactive oxygen species (ROS) which causes photodamage and photoinhibition
Among other examples is the peculiar folding mechanism of light-harvesting complex (LHC) pigmentproteins, binding most of the chlorophyll on earth: these chlorophyll–protein complexes can only fold by incorporating a set of xanthophylls [1] so that each of them comes into close contact with 3–4 chlorophylls [2]

Summary

Introduction

Commentary on: Xanthophyll carotenoids stabilise the association of cyanobacterial chlorophyll synthase with the LHC-like protein HliD. Chlorophylls, essential components for both light harvesting and charge separation reactions in all photosynthetic systems, have a major problem with oxygen: their triplet states react with O2 to yield singlet oxygen, a ROS (reactive oxygen species) which causes photodamage and photoinhibition.

Results

Conclusion