Bacteriophages (phages) are the most widespread and diverse group of viruses that are abundant in microbial ecosystems and specifically infect bacteria. Like other viruses, phages have a nucleic acid genome protected by the proteins of virion. In nature, phages face a wide variety of physical and chemical factors (UV radiation, extreme fluctuations of pH value and temperature). Because of that, the virions of phages are highly robust and stable. This property is very attractive for the development of self-assembled protein nanostructures or phage-like particles.
Phage virion-derived supramolecular nanostructures have a great potential as environment-friendly biomaterials for the development of safe and efficient devices that can be used in technologies and medicine. However, the arsenal of suitable proteins is restricted to only well-studied phages, while the potential of less studied ones remains unknown. Most widespread phages have complex virions designed to recognize and infect host cells. Therefore, prediction of the protein function using only bioinformatic methods can be difficult, and experimental confirmation is needed.
In this study, putative structural proteins of the newly sequenced phages were examined by engineering their recombinant proteins and analyzing the self-assembled protein nanostructures with transmission electron microscope (TEM). For this, we chose three tailed phages from the Myoviridae and Siphoviridae families, which have the icosahedral heads and tails with the fibers attached to them. The putative tail protein of Pantoea agglomerans-infecting phage vB_PagS_MED16, the tail-sheath protein of vB_PagM_AAM22 and the tail-fiber protein from the Escherichia coli-infecting phage vB_EcoM_Alf5 were examined.
Our results show that the recombinant proteins of phage virions adopt characteristic forms resembling those of native phages. Therefore, this methodology is suitable for confirmation of the predicted structural function of phage-encoded proteins. Moreover, the resulting nanostructures can serve as basis for engineering of more complex devices that may be utilized depending on their structural and biochemical characteristics.