Distinct functions of the cyanobacterium Anabaena sp. PCC 7120 paralogs of the Orange Carotenoid Protein N-terminal domain

Adjélé Wilsona, Rocío López-Igual, Ryan L. Leverenz, Matthew R. Melnicki, Céline Bourcier de Carbon, Markus Sutter, Aiko Turmo, François Perreau , Cheryl A. Kerfeld, Diana Kirilovsky
aInstitute for Integrative Biology of the Cell (I2BC), CEA, CNRS, Université Paris-Saclay, Institut de Biologie et Technologies de Saclay (iBiTec-S) 91198 Gif sur Yvette, France

At high irradiance, unbalance of absorbed energy and photosynthesis can be harmful for photosynthetic organisms. In cyanobacteria, the soluble Orange Carotenoid Protein (OCP) is essential in a mechanism down regulating the transfer of energy to the reaction centers by thermal dissipation of the excess absorbed energy at the level of the antenna, the phycobilisome (PB). The OCP is a photoactive protein with a carotenoid as the chromophore serving as light intensity sensor and most probably as energy quencher. In many cyanobacteria, in addition to the entire gene of the OCP, multiple copies encoding homologues to N-terminal domain of the OCP (NTD) are dispersed in their genomes especially in nitrogen-fixing cyanobacteria. Using the cyanobacterium Anabaena (Nostoc) PCC 7120, we show that the four NTD homologous present in its genome which are expressed in the presence or absence of nitrate, attach a carotenoid and have an structure similar to the NTD-OCP [1, 2]. They have distinct functions and belong to a new family of helical carotenoid binding proteins (HCP) [1, 2]. Only All4941 protein (HCP4) is able to bind PBs and quench their fluorescence. All3221 (HCP2) and All4783 (HCP3) are good singlet oxygen (1O2) scavengers as OCP. The All1123 protein (HCP1) is involved in an unknown mechanism different from photoprotection. A gene encoding a homolog to the C-terminal domain (CTDH) is also present near the hcp4 gene. The interaction between All4941 (HCP4) and the CTDH and the construction of a photoactive OCP-like protein including these proteins will be described.

References

[1] Lopez –Igual, Wilson et al., Plant Physiology 2016
[2] Melnicki et al, Molecular Plant 2016, in revision