Functions and Evolution of Lhcb Isoforms Composing LHCII, the Major Light Harvesting Complex of Photosystem II of Green Eukaryotic Organisms

Abstract

Oxygenic photosynthesis provides energy and oxygen for almost all forms of life on earth. This process is based on the energy of photons, which is used to split water and use its electrons to reduce carbon atoms to create organic molecules and thus fix the light energy into a chemical form. Two photosytems working in series are involved in light harvesting and conversion. Both are multi-protein supercomplexes composed of a core complex, where the photochemical reaction takes place, and an antenna system involved in light harvesting. In plants and green algae, the antenna of photosystem II, the photosynthetic complex involved in water splitting, comprises the Light Harvesting Complex II (LHCII) trimers, the most abundant membrane protein on earth. LHCII is composed of highly conserved Lhcb isoforms and all green organisms count a high number of Lhcb. In vascular plants they are classified in three distinct subclasses, Lhcb1, 2 and 3, while in algae and non-vascular plants, these isoforms are less differentiated and called Lhcbm proteins. In this review, we compare LHCII proteins of different organisms, from green algae to angiosperms, and discuss the role of the modifications that occurred through evolution. We highlight the various functions of the different isoforms in photosynthesis, ranging from light harvesting, a common role to all these proteins, to regulations of photosynthesis that rely on specific isoforms.

Isolation and characterization of a large photosystem I–light‐harvesting complex II supercomplex with an additional Lhca1–a4 dimer in Arabidopsis

“…These complexes are composed of different combinations of Lhcbm (in algae and mosses) or Lhcb1–3 (in vascular plants) proteins. All these isoforms present a highly similar sequence and structure (Crepin and Caffarri, ; Pan et al , ): they have three transmembrane domains, bind ~14 chlorophylls (Chls) and have a low Chl a / b ratio of ~1.3/1.4.…”

Unique organization of photosystem II supercomplexes and megacomplexes in Norway spruce

“…The S trimer consists of Lhcb1 and Lhcb2 proteins at different ratios and is attached to C 2 via Lhcb5 and Lhcb4 proteins. The M trimer is formed by one copy of Lhcb3 and two Lhcb1/2 proteins (Caffarri et al ., 2004, 2009; Su et al ., 2017; Crepin and Caffarri, 2018). Lhcb3 is a structurally important component of the M trimer (Caffarri et al ., 2009; Su et al ., 2017), as it can interact with Lhcb6, one of the minor antenna proteins.…”

Composition, phosphorylation and dynamic organization of photosynthetic protein complexes in plant thylakoid membrane

“…41 The three isoforms of the major Lhcb proteins are present in different molar ratios. In Arabidopsis thaliana (Arabidopsis), the Lhcb1:2 : 3 ratio has been estimated to be 7 : 3 : 1 based on proteomic data, 42,43 but the ratio depends on the light condition. Each of the major Lhcb isoforms is present as several subisoforms.…”

“…44,45 For more information about different Lhcb isoforms and their evolution, see the recent review by Crepin and Caffarri. 43 The PSII core complex functions as a dimer and is surrounded by peripheral LHC antenna system. Thus far, the structure of plant (Pisum sativum) PSII-LHCII supercomplex has been resolved by cryo-electron microscopy at 2.7 Å resolution.…”