Prochlorococcus phage ferredoxin: structural characterization and electron transfer to cyanobacterial sulfite reductases.

Ian J Campbell, Jose Luis Olmos, Weijun Xu, Dimithree Kahanda, Joshua T Atkinson, Othneil Noble Sparks, Mitchell D Miller, George N Phillips, George N Bennett, Jonathan J Silberg

The Journal of biological chemistry 2020 Jul 31

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Marine cyanobacteria are infected by phages whose genomes encode ferredoxin (Fd) electron carriers. These Fds are thought to redirect the energy harvested from light to phage-encoded oxidoreductases that enhance viral fitness, but it is unclear how the biophysical properties and partner specificities of phage Fds relate to those of photosynthetic organisms. Here, results of a bioinformatics 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 the cyanobacterium Prochlorococcus marinus, revealed high levels of similarity to cyanobacterial Fds (root mean square deviations of ≤0.5 Å). Additionally, pssm2-Fd exhibited a low midpoint reduction potential (-336 mV versus a standard hydrogen electrode), similar to other photosynthetic Fds, although it had lower thermostability (Tm = 28 °C) than did many other Fds. When expressed in an Escherichia coli strain deficient in sulfite assimilation, pssm2-Fd complemented bacterial growth when coexpressed with a P. marinus sulfite reductase, revealing that pssm2-Fd can transfer electrons to a host protein involved in nutrient assimilation. The high levels of structural similarity with cyanobacterial Fds and reactivity with a host sulfite reductase suggest that phage Fds evolved to transfer electrons to cyanobacterially encoded oxidoreductases. © 2020 Campbell et al.

Citation

Ian J Campbell, Jose Luis Olmos, Weijun Xu, Dimithree Kahanda, Joshua T Atkinson, Othneil Noble Sparks, Mitchell D Miller, George N Phillips, George N Bennett, Jonathan J Silberg. Prochlorococcus phage ferredoxin: structural characterization and electron transfer to cyanobacterial sulfite reductases. The Journal of biological chemistry. 2020 Jul 31;295(31):10610-10623