Chlamydomonas reinhardtii LHCSR1 and LHCSR3 proteins involved in photoprotective non-photochemical quenching have different quenching efficiency and different carotenoid affinity

Abstract

Microalgae are unicellular photosynthetic organisms considered as potential alternative sources for biomass, biofuels or high value products. However, their limited biomass productivity represents a bottleneck that needs to be overcome to meet the applicative potential of these organisms. One of the domestication targets for improving their productivity is the proper balance between photoprotection and light conversion for carbon fixation. In the model organism for green algae, Chlamydomonas reinhardtii, a photoprotective mechanism inducing thermal dissipation of absorbed light energy, called Non-photochemical quenching (NPQ), is activated even at relatively low irradiances, resulting in reduced photosynthetic efficiency. Two pigment binding proteins, LHCSR1 and LHCSR3, were previously reported as the main actors during NPQ induction in C. reinhardtii. While previous work characterized in detail the functional properties of LHCSR3, few information is available for the LHCSR1 subunit. Here, we investigated in vitro the functional properties of LHCSR1 and LHCSR3 subunits: despite high sequence identity, the latter resulted as a stronger quencher compared to the former, explaining its predominant role observed in vivo. Pigment analysis, deconvolution of absorption spectra and structural models of LHCSR1 and LHCR3 suggest that different quenching efficiency is related to a different occupancy of L2 carotenoid binding site.

The Role of Acidic Residues in the C Terminal Tail of the LHCSR3 Protein of Chlamydomonas reinhardtii in Non-Photochemical Quenching

“…Between LHCSR1 and LHCSR3 the latter has been reported to have the main role in a qE induction. 12 , 16 …”

Light Harvesting in Fluctuating Environments: Evolution and Function of Antenna Proteins across Photosynthetic Lineage

“…Light-Harvesting Complex Stress-Related (LhcSR) proteins are found in red (LI818) and green algae (LhcSR) but not in higher plants [23,93]. LhcSR proteins are widely known to regulate thermal energy dissipation (qE type of NPQ) [93][94][95][96]. Four main types of LhcSRs are known to date: LhcSR1, 2 and 3 in Chlamydomonas and mosses and LI818 type in red algae [23].…”

“…Four main types of LhcSRs are known to date: LhcSR1, 2 and 3 in Chlamydomonas and mosses and LI818 type in red algae [23]. LhcSR1 and 3 are reported to perform energy-dependent quenching, but their quenching capability varies due to their different ability to occupy carotenoids in the quenching site (L2 site) in Chlamydomonas reinhardtii [94]. LhcSR1 and LhcSR2 are involved in NPQ in moss Physcomitrella patens [97].…”

“…Among the LhcSRs, the most important one appears to be LhcSR3. Although LhcSR3 is found with both PSI and PSII [101], the energy dissipation is mostly linked with PSII [93,94]. Only one report proposes that LhcSR3 is also responsible for energy dissipation in PSI [102].…”

Structure of the stress-related LHCSR1 complex determined by an integrated computational strategy

“…Based on the conserved Mg binding sites and previous literature 14,[17][18][19] , Chls 602, 603, 609, 610, and 612 should be present on the stromal side of the complex, and Chls 604 and 613 should be bound to the lumenal side. Also Chl a611 is thought to be present 13,14,22 , even if it is not directly bound to a protein residue. For this reason, we retained also Chl a611 in the LHCSR model, along with its axial ligand, the DPPC lipid 16 .…”