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Structure of phage P22 cell envelope–penetrating needle


Bacteriophage P22 infects Salmonella enterica by injecting its genetic material through the cell envelope. During infection, a specialized tail needle, gp26, is injected into the host, likely piercing a hole in the host cell envelope. The 2.1-Å crystal structure of gp26 reveals a 240-Å elongated protein fiber formed by two trimeric coiled-coil domains interrupted by a triple β-helix. The N terminus of gp26 plugs the portal protein channel, retaining the genetic material inside the virion. The C-terminal tip of the fiber exposes β-hairpins with hydrophobic tips similar to those seen in class II fusion peptides. The α-helical core connecting these two functionally polarized tips presents four trimerization octads with consensus sequence IXXLXXXV. The slender conformation of the gp26 fiber minimizes the surface exposed to solvent, which is consistent with the idea that gp26 traverses the cell envelope lipid bilayers.

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Figure 1: Three-dimensional structure of phage P22 tail needle gp26.
Figure 2: Helical core of gp26.
Figure 3: Comparative analysis of gp26 helical core (domain II) and the ectodomain of influenza hemagglutinin.
Figure 4: The basic C-terminal tip of gp26 may be involved in membrane penetration.
Figure 5: Fitting of tail needle gp26 into the asymmetric cryo-EM reconstruction of mature P22 phage.

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We thank N. Walker for technical help. We are grateful to V. Stojanoff at the NSLS and to the macCHESS staff for beam time and assistance in data collection. This work was supported in part by US National Science Foundation grant MCB-990526 to S.C.

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Authors and Affiliations



A.S.O. and G.C. contributed to the structural and biochemical studies. S.C. participated in the design and coordination of the study. A.S.O., S.C. and G.C. wrote the manuscript.

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Correspondence to Gino Cingolani.

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Olia, A., Casjens, S. & Cingolani, G. Structure of phage P22 cell envelope–penetrating needle. Nat Struct Mol Biol 14, 1221–1226 (2007).

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