Bacteriophages – viruses that infect bacteria – are found everywhere and in huge numbers. Their taxonomy has not yet been established, but most bacteriophages are classified as Caudovirales. The genome of such viruses is represented by a short double-stranded DNA enclosed in an icosahedral protein shell. A tail is attached to this head, with which the bacteriophage attaches to the host cell and infects.
The tail is formed from many proteins, folded into a spiral structure with a cavity inside. Usually it is not too impressive in length, only several times the size of the virus head. However, the new phage P74-26, described by biologists from the University of Massachusetts, stands out against the general background. Its tail reaches an incredible length, almost a micrometer, which is comparable to the thickness of the web threads. About this Brian Kelch (Brian Kelch) and his colleagues write in an article, published V Journal of Biological Chemistry.
Because of its record long tail, the virus received the unofficial name “Rapunzel” – in honor of the fabulous heroines with very long hair. In addition, P74-26 stands out for its high resistance to extreme environmental conditions. The phage is found in hot springs, where temperatures can exceed 80 degrees Celsius, and infects the extremophile bacteria that live there.
The scientists studied the process of self-assembly of the P74-26 long tail from individual proteins using cryoelectron microscopy. “I like to compare it to Lego,” said Brian Kelch. – Such parts have bumps on one side and depressions on the opposite. But imagine that at first these cavities are closed and become accessible only when the part is already docked to the previous one. This shape change plays an important role in the regulation of self-assembly.”
The scientists also noted that the tail of P74-26 consists of fewer different proteins than usual. This may be due to the fact that some of these molecules were the result of the fusion of smaller proteins with each other. Perhaps this feature is one of the elements that ensure the stability of the virus structure in hot springs. “The long tail is made up of larger and more stable blocks,” Professor Kelch added.