Light-harvesting photosynthetic tetrapyrrole chromophore-protein from the phycobiliprotein complex. Heterododecamer of 6 alpha and 6 beta chains. The basic functional unit of phycobiliproteins is a ring-shaped hexamer formed from two back-to-back trimers contacting via the alpha chain subunits. The trimers are composed of alpha/beta subunit heterodimers arranged around a three-fold axis of symmetry. The phycoerythrins also contain a gamma subunit which is located in the center of the hexamer. Forms the periphery of the phycobilisome rod. Contains two covalently linked phycoerythrobilin chromophores and one covalently linked phycourobilin chromophore. In the PDB entry, the bilins are named as phycocyanobilins although the modeled compounds correspond to phycoerythrobilins. The light-harvesting antenna system in red algae and cyanobacteria is formed of phycobilisomes. These are composed of the phycobiliproteins phycoerythrin (CPE), phycocyanin (CPC) and allophycocyanin (APC). Cyanobacteria also contain phycoerythrocyanin (PCC). The phycobiliproteins all share the same subunit composition and organization with variations in the covalently bound open-chain tetrapyrrole chromophores. The phycobiliprotein complexes are arranged sequentially in antenna complexes linked by linker proteins with CPE at the periphery, CPC in the middle and APC at the core feeding to the photosynthetic reaction center. Belongs to the phycobiliprotein family.