PI Roberto Bassi (VER) and ESR Giulio Stella (UPMC) publish in The Journal of Biological Chemistry
Identification of pH-sensing Sites in the Light Harvesting Complex Stress-related 3 Protein Essential for Triggering Non-photochemical Quenching in Chlamydomonas reinhardtii
Light harvesting complex stress-related 3 (LHCSR3) is the protein essential for photoprotective excess energy dissipation (non-photochemical quenching, NPQ) in the model green alga Chlamydomonas reinhardtii. Activation of NPQ requires low pH in the thylakoid lumen, which is induced in excess light conditions and sensed by lumen-exposed acidic residues. In this work we have used site-specific mutagenesis in vivoand in vitro for identification of the residues in LHCSR3 that are responsible for sensing lumen pH. Lumen-exposed protonatable residues, aspartate and glutamate, were mutated to asparagine and glutamine, respectively. By expression in a mutant lacking all LHCSR isoforms, residues Asp117, Glu221, and Glu224 were shown to be essential for LHCSR3-dependent NPQ induction in C. reinhardtii. Analysis of recombinant proteins carrying the same mutations refolded in vitro with pigments showed that the capacity of responding to low pH by decreasing the fluorescence lifetime, present in the wild-type protein, was lost. Consistent with a role in pH sensing, the mutations led to a substantial reduction in binding the NPQ inhibitor dicyclohexylcarbodiimide.
Ballottari, Matteo, Thuy B. Truong, Eleonora De Re, Erika Erickson, Giulio R. Stella, Graham R. Fleming, Roberto Bassi, and Krishna K. Niyogi. "Identification of pH-sensing sites in the Light Harvesting Complex Stress-Related 3 protein essential for triggering non-photochemical quenching in Chlamydomonas reinhardtii." Journal of Biological Chemistry 291, no. 14 (2016): 7334-7346.
Author: Fiona Moejes