Book of Abstracts: Albany 2007
June 19-23 2007
Atomic Structure of Bacteriophage P22 Cell-wall Penetrating Tail Needle Gp26
Bacteriophages infect prokaryotic cells by injecting their genome through the bacterial cell wall. In gram-negative bacteria like Salmonella enterica, the cell wall is ∼150Å thick barrier formed by two lipid bilayers surrounding a thin layer of peptidoglycan. To efficiently penetrate the Salmonella cell wall, bacteriophage P22 uses a specialized tail needle, gp26, which also serves as portal protein closure factor, necessary to retain the viral genome inside the capsid. The 2.0Å crystal structure of the tail needle gp26 reveals a 240Å elongated protein fiber formed by two trimeric α-helical coil-coiled domains interrupted by a triple-β helix. The first coil-coiled domain of gp26 spans 165Å and is held together by four trimerization octads, which confer a slender and stiff conformation to the fiber. This helical core relates gp26 to class I membrane fusion proteins, while the C-terminal helical domain exposes β-hairpins with hydrophobic tips, homologous to those seen in class II fusion peptides. The extended topology of the trimer minimizes the surface exposed to solvent that is largely hydrophobic. This is consistent with the knowledge that gp26 is ejected through the bacterial cell wall during infection.
In the order to understand how the 3D-structure of gp26 correlates with its putative function of cell-wall penetrating devise, we undertook a detailed analysis of gp26 folding, oligomerization, and chemical stability. Remarkably we found that the tail-needle gp26 is characterized by exceedingly high structural stability. Gp26 fibers melt irreversibly in ∼7M Guanidine-HCl, are insensitive to phenol extraction and retain a folded trimeric quaternary structure in anhydrous environment when lyophilized. Using the crystal structure as template, we have rationally engineered the helical core of gp26 to fabricate longer fibers of pre-programmable length. Our initial results indicate that gp26-derived fibers are significantly more stable than the wild type protein and represent an attractive and novel bio-material for future application in biotechnology.
1Department of Biochemistry and Molecular Biology