Viral contractile tail ejection system (kw:KW-1242)

The long and contractile tail of Myoviridae acts as a molecular machine that ejects the viral DNA from the capsid into the host cell cytoplasm. The ejection system consists of a baseplate, a central tube and an external contractile sheath .

Upon binding to the host cell surface, the baseplate changes its conformation and triggers sheath contraction, driving the rigid internal tail tube through the cell envelope.

The source of the forces that drive viral genome ejection is probably in part due to osmotic pressure imbalance between the virus inside and the host cytoplasm .

Gram(-) hosts:

1. Attachment to a host cell outer membrane (OM) receptor.
2. Tail sheath contraction. Ejection of the internal rigid tube through the OM using the puncturing device.
3. Virion-associated exolysin (if present) hydrolyzes the peptidoglycan layer. Ejection of the internal rigid tube through the cell wall.
4. Complete contraction and ejection of the internal rigid tube. Fusion with the inner membrane.
5. Viral DNA translocation into host cytoplasm.
   
   

Gram(+) hosts:

1. Attachment to a host cell wall receptor.
2. Tail sheath contraction. Virion-associated exolysin (if present) hydrolyzes the peptidoglycan layer. Ejection of the internal rigid tube through the cell wall.
3. Complete contraction and ejection of the internal rigid tube. Possible ejection of the tape-measure protein and opening of the proximal plug. Fusion with the plasma membrane.
4. Viral DNA translocation into host cytoplasm.