Cyanobacteria perform oxygenic photosynthesis and can be found in almost every habitat on earth. They are infected by specific viruses, cyanophages. During phage infection, key metabolic pathways of the cyanobacterial host (such as photosynthesis, carbon-, and fatty acid- metabolism) are significantly altered. So-called auxiliary metabolic genes (AMGs) encoded in the genome of the infecting phage are believed to contribute to the takeover of the cyanobacterial cell by maintaining the host metabolism during the infection cycle. AMGs are frequently found in cyanophage genomes.1,2 We are investigating the role of a particular AMG, the plastocyanin-like gene petE from the cyanophage Syn9. Plastocyanins are small blue copper proteins that transfer electrons from the cytochrome b6f complex to photosystem I and are commonly found in most cyanobacteria, algae, and plants.3
To verify the functionality of the phage gene, Syn9petE was heterologously expressed in E. coli. The purified recombinant protein displayed the blue colour typical for plastocyanins and an absorption maximum at ~600 nm. The protein can shift between different redox states. Furthermore, EPR spectroscopy confirmed its identity as a type I copper-binding protein and a midpoint potential of 286 mV was determined by redox titration. In parallel, a recombinant Syn9 phage lacking a functional petE was generated. In parallel, a recombinant Syn9 cyanophage lacking a functional copy of petE was generated. Recombinant phage particles were first enriched, subsequently purified and assessed for their efficiency in infection and viral particle production.
In summary, our objective is to understand the role of cyanophage-encoded plastocyanin, its importance for phage progeny production and to elucidate how cyanophage proteins interact with host metabolism.
References:
L.R. Thompson, Q. Zeng, L. Kelly, K.H. Huang, A.U. Singer, J. Stubbe, S.W. Chisholm.
Proc Natl Acad Sci U S A., 2011, 108(39), E757-64.D. Lindell, J.D. Jaffe, Z.I. Johnson, G.M. Church, S.W. Chisholm.
Nature, 2005, 438(7064), 86-89.E.L. Gross.
Photosynthesis Research, 1993, 37(2), 103-116.