Buth, S. A. | Search bioRxiv

bioRxiv2025

The spike tip protein of bacteriophage T4

Contractile injection systems (CISs) - bacteriophage tails, tailocins, and bacterial type VI secretion systems - penetrate the envelope of the target cell by employing a contractile sheath-rigid tube mechanism. The membrane-attacking end of the tube carries a spike-shaped complex that ends with a spike tip. In bacteriophage P2, the spike and spike tip proteins are fused, and we used this phage to show that sheath contraction results in the translocation of the spike into the periplasm of the host cell. In bacteriophage T4, the spike and spike tip proteins are encoded by different genes. We show that the ORFan gene 5.4 codes for the spike tip protein of bacteriophage T4. Using an amber nonsense mutation, we show that the gp5.4 protein is dispensable for bacteriophage T4 particle assembly but essential for bacteriophage fitness and infection of bacteria with truncated lipopolysaccharides.

molecular biology↗

bioRxiv2023

Function of the bacteriophage P2 baseplate central spike Apex domain in the infection process

The contractile tail of bacteriophage P2 functions to drive the tail tube across the outer membrane of its host bacterium, a prerequisite event for subsequent translocation of phage genomic DNA into the host cell. The tube is equipped with a spike-shaped protein (product of P2 gene V, gpV or Spike) that contains a membrane-attacking Apex domain carrying a centrally positioned Fe ion. The ion is enclosed in a histidine cage that is formed by three symmetry-related copies of a conserved HxH (histidine, any residue, histidine) sequence motif. Here, we used solution biophysics and X-ray crystallography to characterize the structure and properties of Spike mutants in which the Apex domain was either deleted or its histidine cage was either destroyed or replaced with a hydrophobic core. We found that the Apex domain is not required for the folding of full-length gpV or its middle intertwined {beta}-helical domain. Furthermore, despite its high conservation, the Apex domain is dispensable for infection in laboratory conditions. Collectively, our results show that the diameter of the Spike but not the nature of its Apex domain determines the efficiency of infection, which further strengthens the earlier hypothesis of a drill bit-like function of the Spike in host envelope disruption.

molecular biology↗