Underlying data for characterization of phycocyanobilin (PCB) biosynthesis in Galdieria sulphuraria

This dataset contains data for studies of phycocyanobilin (PCB) synthesis in the red alga Galdieria sulphuraria. Red algae such as G. sulphuraria utilize phycobilisomes for light harvesting. The phycobilisomes of early-branching organisms such as G. sulphuraria or Cyanidioschyzon merolae contain PCB chromophores but not phycoerythrobilin (PEB), in contrast to the phycobilisomes of other red algae. The studies reported in this dataset examine biosynthesis of PCB in G. sulphuraria and C. merolae, starting from biliverdin IX-alpha (BV), the last known common precursor for PCB and PEB. In cyanobacteria, phages, green algae, and land plants, conversion of BV into PCB or PEB is carried out by a family of enzymes called ferredoxin-dependent bilin reductases (FDBRs). The current studies demonstrate that G. sulphuraria, but not C. merolae, require the action of an additional isomerase to synthesize PCB.

Deposited data include phylogenetic analyses, data for in vitro characterization of recombinantly expressed FDBRs from G. sulphuraria and C. merolae, and data for fractionation of G. sulphuraria extracts and isomerase assays on the resulting enriched fraction. The phylogenetic analyses demonstrates that G. sulphuraria has two FDBRs, GsPEBA and GsPEBB, whereas C. merolae has a single FDBR, CmPCYA. CmPCYA would be expected to convert BV into PCB, whereas GsPEBA would be expected to convert BV into 15,16-dihydrobiliverdin (15,16-DHBV) and GsPEBB would then convert 15,16-DHBV into PEB rather than PCB. In vitro characterization demonstrates that all three FDBRs carry out the expected reactions, meaning that the G. sulphuraria enzymes produce PEB but the phycobilisomes contain PCB. This conundrum is resolved by demonstrating the existence of an isomerase in G. sulphuraria extracts that can convert PEB into PCB.