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Proc Natl Acad Sci U S A. 2009 Mar 17;106(11):4160-5. doi: 10.1073/pnas.0900044106. Epub 2009 Feb 27.

The phage lambda major tail protein structure reveals a common evolution for long-tailed phages and the type VI bacterial secretion system.

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Department of Biochemistry, University of Toronto, Medical Sciences Building, Toronto, ON M5S 1A8, Canada.


Most bacteriophages possess long tails, which serve as the conduit for genome delivery. We report the solution structure of the N-terminal domain of gpV, the protein comprising the major portion of the noncontractile phage lambda tail tube. This structure is very similar to a previously solved tail tube protein from a contractile-tailed phage, providing the first direct evidence of an evolutionary connection between these 2 distinct types of phage tails. A remarkable structural similarity is also seen to Hcp1, a component of the bacterial type VI secretion system. The hexameric structure of Hcp1 and its ability to form long tubes are strikingly reminiscent of gpV when it is polymerized into a tail tube. These data coupled with other similarities between phage and type VI secretion proteins support an evolutionary relationship between these systems. Using Hcp1 as a model, we propose a polymerization mechanism for gpV involving several disorder-to-order transitions.

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