RT Journal Article SR Electronic T1 Prochlorococcus phage ferredoxin: structural characterization and electron transfer to cyanobacterial sulfite reductases JF bioRxiv FD Cold Spring Harbor Laboratory SP 2020.02.07.937771 DO 10.1101/2020.02.07.937771 A1 Ian J. Campbell A1 Jose L. Olmos, Jr. A1 Weijun Xu A1 Dimithree Kahanda A1 Joshua T. Atkinson A1 Othneil N. Sparks A1 Mitchell D. Miller A1 George N. Phillips, Jr. A1 George N. Bennett A1 Jonathan J. Silberg YR 2020 UL http://biorxiv.org/content/early/2020/05/05/2020.02.07.937771.abstract AB Marine cyanobacteria are infected by phage whose genomes encode ferredoxin (Fd) electron carriers. While these Fds are thought to redirect the energy harvested from light to phage-encoded oxidoreductases that enhance viral fitness, it is not clear how the biophysical properties and partner specificities of phage Fds relate to those in photosynthetic organisms. Bioinformatic analysis using a sequence similarity network revealed that phage Fds are most closely related to cyanobacterial Fds that transfer electrons from photosystems to oxidoreductases involved in nutrient assimilation. Structural analysis of myovirus P-SSM2 Fd (pssm2-Fd), which infects Prochlorococcus marinus, revealed high similarity to cyanobacterial Fds (≤0.5 Å RMSD). Additionally, pssm2-Fd exhibits a low midpoint reduction potential (−336 mV vs. SHE) similar to other photosynthetic Fds, albeit lower thermostability (Tm = 28°C) than many Fds. When expressed in an Escherichia coli strain with a sulfite assimilation defect, pssm2-Fd complemented growth when coexpressed with a Prochlorococcus marinus sulfite reductase, revealing that pssm2-Fd can transfer electrons to a host protein involved in nutrient assimilation. The high structural similarity with cyanobacterial Fds and reactivity with a host sulfite reductase suggest that phage Fds evolved to transfer electrons to cyanobacterial-encoded oxidoreductases.Competing Interest StatementThe authors have declared no competing interest.aTcanhydrotetracyclineDTTdithiothreitolETelectron transferFdferredoxinFNRFd-NADP reductaseGcpE4-Hydroxy-3-methylbut-2-enyl diphosphate synthaseGSglutamate synthaseHOheme oxygenaseIPTGisopropyl β-D-1-thiogalactopyranosideLBlysogeny brothml-Fd1Mastigocladus laminosus Fd 1NIRnitrite reductasensp-Fd1Nostoc sp. PCC 7119 Fd 1ODoptical densityORFsopen reading framesPcyAphycocyanobilin:Fd oxidoreductasePebSphycoerythrobilin synthasepm9211-Fd1Prochlorococcus marinus MIT9211 Fd 1pm9211-SIRProchlorococcus marinus MIT9211 SIRpmN1-Fd1Prochlorococcus marinus NATL1A Fd 1pmN2-Fd1Prochlorococcus marinus NATL2A Fd 1pmN2-SIRProchlorococcus marinus NATL2A SIRPSIphotosystem Ipssm2-Fdmyovirus P-SSM2 FdRFPred fluorescent proteins6803-Fd1Synechocystis sp. PCC 6803 Fd 1SHEstandard hydrogen electrodeSIRsulfite reductaseSSNsequence similarity networkte-Fd1Thermosynechococcus elongatus Fd 1zm-Fd1Zea mays Fd 1zm-FNRZea mays FNRzm-SIRZea mays SIR