Beta subunits of phycocyanin, phycoerythrin and phycoerythrocyanin; phycobilisome rod components
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 includes the beta subunits of Cryptophyte phycobiliproteins which represent another type of biliprotein antenna with different structure and organization. The beta subunits of cryptophyte PBPs share a high degree of sequence identity with both the alpha and beta subunits of the cyanobacterial and red algal PBPs, however the alpha cryptophyte subunits are shorter, and unrelated. There is only one type of PBP present in a single species, either phycocyanin or phycoerythrin, but not allophycocyanin. Structurally, phycoerythrin in cryptophytes is an alpha1alpha2betabeta dimer and not a trimer as in the PBS.
Feature 1:chromophore binding site 1 [chemical binding site]
Evidence:
Comment:There are two conserved chromophore binding sites in this subfamily, one located around position Cys-82 and the other at position Cys-158. This binding site represents the former.
Structure:1B8D: Griffithsia monilis R-phycoerythrin beta binds phycoerythrobilin at position Cys-82; contacts at 4A
Comment:Cys-84 is the conserved attachment site present in cyanobacterial and red algal phycobiliproteins, and in the beta-subunits of cryptophyte biliproteins. The actual position of the central conserved Cys varies from positions 81 to 84.
Comment:Griffithsia monilis R-phycoerythrin beta has two covalently bound phycoerythrobilins at positions Cys-82 and Cys-158 and one phycourobilin doubly linked to Cys-50 and Cys-61. Cryptophyte Rhodomonas CS24 phycoerythrin B subunit has a phycoerythrobilin at each of these positions.
Jiyao W et al.(2023). "The conserved domain database in 2023.",