Abstract
Phycobilisomes (PBSs) are light-harvesting complexes found in
cyanobacteria and red algae. These organisms degrade PBS under
nitrogen-limited conditions. In cyanobacteria, the small NblA protein
plays a key role in this process; it acts as an adaptor protein to promote
the interaction of a Clp protease with phycobiliproteins. There is an nblA-like
gene (ycf18) the chloroplast genomes of most red algae. Recently
additional nblA genes were identified in the nuclear genomes of Porphyra
umbilicalis, Pyropia yezoensis, Gracilariopsis chorda,
Galdieria sulphuraria, Cyanidioschyzon merolae, and Porphyridium
purpureum. However, their function remains unknown. This review
focused on two types of NblA in red algae: Ycf18 and NblA. Typically, both
contain an intact NblA motif, although P. purpureum Ycf18
does not. Ycf18 is composed of approximately 60 amino acids, although five
NblAs were predicted to be located in chloroplasts, and to be larger (88
to 227 amino acids) due to disordered regions at the N- and C-terminal
ends. Cyanobacterial nblA gene existing as single copy in the
genome acts as a homodimer. The occurrence of two nblA
genes in these red algae suggested that a heterodimer may play a role in
PBS degradation in red algae. This will be discussed from the perspective
of the protein structure of NblA.
