phycobilisomes (PBSs) are the main light-harvesting complex in cyanobacteria and red algae. In general, they consist of a central core and surrounding rods and function to harvest and channel light energy toward the photosynthetic reaction centers within the membrane. They are comprised of phycobiliproteins/chromophorylated proteins (PBPs) maintained together by linker polypeptides. PBPs have different numbers of chromophores, and the basic monomer component (alpha/beta heterodimers) can further oligomerize to ring-shaped trimers (heterohexamers) and hexamers (heterododecamers). Stacked PBP hexamers form both the core and the rods of the PBS; the core is mainly made up by allophycocyanin (APC) while the rods can be composed of the PBPs phycoerythrin (PE), phycocyanin (PC) and phycoerythrocyanin (PEC). This family also contains allophycocyanin-like (Apl) proteins, which conserve the residues critical for chromophore interactions, but may not maintain the proper alpha-beta subunit interactions and tertiary structure of PBPs. The genes encoding the Apl proteins cluster with light-responsive regulatory components, so these may have photoresponsive regulatory role(s). Included in this family is the PBP-like domain of the core-membrane linker polypeptide (LCM). The LCM serves both as a terminal energy acceptor and as a linker polypeptide. Its single phycocyanobilin (PCB) chromophore is one of two terminal energy transmitters, and transfers excitations from the hundreds of chromophores of the PBS to the RCs. This family also includes some proteins which have glutathione-S-transferases (GST) domains N-terminal to this PBP-like domain.
Feature 1:chromophore binding site [chemical binding site]
Evidence:
Comment:A conserved cysteine residue, present in cyanobacterial and red algal phycobiliproteins, and in the beta-subunits of cryptophyte biliproteins, is involved in covalent bonding with the chromophore. The actual position of the central conserved Cys varies from positions 81 to 84.
Jiyao W et al.(2023). "The conserved domain database in 2023.",