ScholarWorks@UNO

Characterization of the Protein Encoded by unk9, a Conserved Gene of Unknown Function in Synechococcus sp. RS9916

Light harvesting antennae complexes of photosystem II, phycobilisomes, are anchored to the thylakoid membranes in cyanobacteria. These phycobilisomes are comprised of rods and a core containing phycobiliproteins (PBP) and linker polypeptides. The outer rods of the PBP have red protein-pigment complexes called phycoerythrin (PE), comprised of α- and β-subunits. Some species of Synechococcus contain two types of PE in the distal part of their rods, phycoerythrin class I (PE I) and phycoerythrin class II (PE II). Both PE I and PEII bind phycoerythrobilin (PEB) and PE II binds both phycoerythrobilin (PEB) and phycourobilin (PUB). These bilins are bound to PE due to the enzymatic activity of phycobilin lyases. The operon encoding various PE II-specific genes has a conserved gene of unknown function called unk9 (Six et al., 2007). The 332bp gene, unk9, lies adjacent to mpeY in the genome and encodes a protein which is uncharacterized, but is conserved in all PE-II containing organisms. A histidine-tagged (HT) form of unk9 was amplified by PCR and cloned in the pCOLA vector in order to produce recombinant HT-UNK9 protein in E. coli. The HT-UNK9 protein produced in E. coli was soluble. Because the unk9 gene is adjacent to mpeY, we hypothesized that his-tagged Unk9 may interact with other putative lyases such as MpeY or MpeU, affecting their activity. Recombinant protein co-expression experiments were completed to determine the function of Unk9. Results from this project will be presented. References: Six, Christophe, et al. "Diversity and evolution of phycobilisomes in marine Synechococcus spp.: a comparative genomics study." Genome Biol 8.12 (2007): R259.