Elucidating the origins of phycocyanobilin biosynthesis and phycobiliproteins

Terrestrial ecosystems and human societies depend on oxygenic photosynthesis, which began to reshape our atmosphere approximately 2.5 billion years ago. The earliest known organisms carrying out oxygenic photosynthesis are the cyanobacteria, which use large complexes of phycobiliproteins as light-harvesting antennae. Phycobiliproteins rely on phycocyanobilin (PCB), a linear tetrapyrrole (bilin) chromophore, as the light-harvesting pigment that transfers absorbed light energy from phycobilisomes to the chlorophyll-based photosynthetic apparatus. Cyanobacteria synthesize PCB from heme in two steps: A heme oxygenase converts heme into biliverdin IXα (BV), and the ferredoxin-dependent bilin reductase (FDBR) PcyA then converts BV into PCB. In the current work, we examine the origins of this pathway. We demonstrate that PcyA evolved from pre-PcyA proteins found in nonphotosynthetic bacteria and that pre-PcyA enzymes are active FDBRs that do not yield PCB. Pre-PcyA genes are associated with tw..., Absorption spectra were collected on Cary 50 or Cary 60 spectrophotometers and were exported from the Cary software in .csv format. They were then processed using an in-house script to remove metadata and were plotted, analyzed, and prepared for presentation in Kaleidagraph. Presented spectra were exported from Kaleidagraph as tab-delimited text files with unix newlines and are deposited in that format. Some spectra were subtracted from each other to generate difference spectra and/or normalized to facilitate comparison; such spectra are presented separately in the same format. Some samples were characterized using a standard acid denaturation assay, and peak wavelengths from these spectra were plotted for comparison to references with known bilin composition. The reference and unknown values are deposited together as tab-delimited text files for short and long wavelengths.
Circular dichroism spectra were collected on an Applied Photophysics Chirascan and were converted to tab-delimited...,
All files are reported as flat text files with unix newlines. A README.txt is included with this submission.