Structural framework for DNA translocation via the viral portal protein
2007
Lebedev, Andrey A. | Krause, Margret H. | Isidro, Anabela L. | Vagin, Alexei A. | Orlova, Elena V. | Turner, Joanne | Dodson, Eleanor J. | Tavares, Paulo | Antson, Alfred A.
Tailed bacteriophages and herpesviruses load their capsids with DNA through a tunnel formed by the portal protein assembly. Here we describe the X-ray structure of the bacteriophage SPP1 portal protein in its isolated 13-subunit form and the pseudoatomic structure of a 12-subunit assembly. The first defines the DNA-interacting segments ( tunnel loops) that pack tightly against each other forming the most constricted part of the tunnel; the second shows that the functional dodecameric state must induce variability in the loop positions. Structural observations together with geometrical constraints dictate that in the portal-DNA complex, the loops form an undulating belt that fits and tightly embraces the helical DNA, suggesting that DNA translocation is accompanied by a 'mexican wave' of positional and conformational changes propagating sequentially along this belt.
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