Regulating Light-Harvesting Protein Assembly through Engineered Trimers of Phycocyanin and Allophycocyanin

Abstract

Phycobiliproteins form oligomeric assemblies essential for photosynthetic light harvesting. Here, we engineered phycocyanin (TeCPC) and allophycocyanin (TeAPC) from Thermosynechococcus elongatus to stabilize defined trimers by inhibiting hexamer formation. Structure-guided substitutions at conserved glycine residues (TeCPC G29R, TeAPC G21R) introduce steric hindrance at the hexamer interface. Recombinant expression in Escherichia coli produced holoproteins with native-like chromophorylation. Biophysical and structural analyses confirmed homogeneous trimer formation and absence of higher-order assemblies. Thermal measurements indicated cooperative unfolding, supporting structural uniformity. These engineered trimers provide robust models for studying energy transfer in phycobiliproteins.