Evolution of a divinyl chlorophyll-based photosystem in Prochlorococcus

Area of Science:

• Photosynthesis research
• Molecular evolution
• Biochemistry

Background:

• Evolution of photosynthesis involves acquiring new pigments and adapting pigment-binding proteins.
• Prochlorococcus uniquely uses divinyl chlorophyll (DVChl), unlike other organisms using monovinyl chlorophyll.
• Cyanobacterial mutants accumulating DVChl typically die, indicating a need for concurrent protein evolution.

Purpose of the Study:

• To investigate the coevolution of chlorophyll (Chl) and Chl-binding proteins during the development of DVChl-based photosystems.
• To understand the role of specific amino acid substitutions in the D1 protein for DVChl adaptation.

Main Methods:

• Comparative analysis of Chl-binding protein amino acid sequences between Prochlorococcus and other photosynthetic organisms.
• Site-directed mutagenesis of the D1 protein in Synechocystis sp. PCC6803 to mimic Prochlorococcus substitutions (V205M).
• Transformation of Synechocystis dvr mutant with the mutated D1 protein construct and assessment of light tolerance.

Main Results:

• Identified specific D1 protein residues (V205 and G282 in standard photosystems) substituted in Prochlorococcus (M205 and C282).
• Mutating V205 to M205 in Synechocystis D1 protein conferred light tolerance under medium-light conditions.
• The substitution G282C provided additional light tolerance, highlighting the importance of these changes for DVChl photosystems.

Conclusions:

• Amino acid substitutions in the D1 protein are crucial for the functional establishment of DVChl-based photosystems.
• These adaptations in pigment-binding proteins likely coevolved with the acquisition of DVChl in Prochlorococcus.
• The study elucidates the molecular mechanisms underlying the evolution of novel photosynthetic systems.