Structural highlights
Publication Abstract from PubMedPodoviridae are double stranded DNA bacteriophages that use short, non-contractile tails to adsorb to the host cell surface. Within the tail apparatus of P22-like phages, a dedicated fiber known as the 'tail needle' likely functions as a cell envelope-penetrating device to promote ejection of viral DNA inside the host. In Sf6, a P22-like phage that infects Shigella flexneri, the tail needle presents a C-terminal globular knob. This knob, absent in phage P22 but shared in other members of the P22-like genus, represents the outermost exposed tip of the virion that contacts the host cell surface. Here, we report a crystal structure of the Sf6 tail needle knob determined at 1.0 A resolution. The structure reveals a trimeric globular domain of the TNF fold structurally superimposable with that of the tailless phage PRD1 spike protein P5 and the adenovirus knob, domains that in both viruses function in receptor binding. However, P22-like phages are not known to utilize a protein receptor and are thought to directly penetrate the host surface. At 1.0 A resolution, we identified three equivalents of L-Glutamic acid (L-Glu) bound to each subunit interface. Although intimately bound to the protein, L-Glu does not increase the structural stability of the trimer nor it affects its ability to self-trimerize in vitro. In analogy to P22 gp26, we suggest the tail needle of phage Sf6 is ejected through the bacterial cell envelope during infection and its C-terminal knob is threaded through peptidoglycan (PG) pores formed by glycan strands. Atomic structure of bacteriophage Sf6 tail needle knob.,Bhardwaj A, Molineux IJ, Casjens SR, Cingolani G J Biol Chem. 2011 Jun 25. PMID:21705802[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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