Analysis of the cell-puncturing device also reveals a structure that may hold potential for applications in nanotechnology, such as microscopic probes, Rossmann says.
"This a very stable structure that looks like a small stylus," he says. "It might be useful as a probe in an atomic force microscope, which employs a probe of molecular dimension."
The T4 virus consists of an elongated head, which carries the virus' genetic material, and a tail made up of a hexagonal baseplate and six leg-type structures, called long-tail and short-tail fibers.
In the study, the Purdue group analyzed atom-by-atom the structure of the virus' baseplate. The baseplate is the key component of the virus, Rossmann says, serving as a "nerve center" and sending signals to and from the virus' head and tail fibers.
While transmitting its messages, the baseplate also prepares the virus machinery to eject its DNA into the host cell.
"A whole series of events are required to recognize, attach and confirm the attachment, and then contract so that the viral DNA can be ejected into the host," Rossmann says. "It's a very complicated system for infecting a cell."
The viral machine works as follows:
The virus uses its long-tail fibers to recognize its host and to send a signal back to the baseplate. Once the signal is received, the short-tail fibers help anchor the baseplate into the cell surface receptors. As the virus sinks down onto the surface, the baseplate undergoes a change shifting from a hexagon to a star-shaped structure. At this time, the whole tail structure shrinks and widens, bringing the internal pin-like tube in contact with the outer membrane of the E. coli cell. As the tail tube punctures the outer and inner membranes of the E. coli cell, the virus' DNA is in
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