P-SCSP1 is a newly found group of T7-like cyanobacteria phages (cyanophages), belonging to the MPP (marine picocyanobacterial podovirus)-C class. The cyanophage profoundly impacts the whole biosphere by infecting cyanobacteria and deserves explicit investigation. However, the high-resolution structures of cyanophages are not reported yet. The assembling and evolutionary mechanisms of cyanophages are not clear either. Here, we reported the near-atomic structures of the P-SCSP1 capsid protein and portal-tail complex via cryo-electron microscopy (cryo-EM) single-particle analysis (SPA). The atomic models showed the organization of 420 capsid proteins, 12 portal proteins, and 36 tail proteins from the mature phage particles and revealed the mechanisms of P-SCSP1 assembling. The interactions...[ Read more ]

P-SCSP1 is a newly found group of T7-like cyanobacteria phages (cyanophages), belonging to the MPP (marine picocyanobacterial podovirus)-C class. The cyanophage profoundly impacts the whole biosphere by infecting cyanobacteria and deserves explicit investigation. However, the high-resolution structures of cyanophages are not reported yet. The assembling and evolutionary mechanisms of cyanophages are not clear either. Here, we reported the near-atomic structures of the P-SCSP1 capsid protein and portal-tail complex via cryo-electron microscopy (cryo-EM) single-particle analysis (SPA). The atomic models showed the organization of 420 capsid proteins, 12 portal proteins, and 36 tail proteins from the mature phage particles and revealed the mechanisms of P-SCSP1 assembling. The interactions among the portal-tail complex proteins strongly explain how subunits form a stable and functional cyanophage tail. The DNA gating system of cyanophage was also firstly revealed by our structural analysis. Combined with our results, we proposed a new DNA gating model of T7-like cyanophage at the initial stage of infection. Meanwhile, we introduced a new evolutionary classification method of the T7-like phages based on the structure comparison, which pointed out that P-SCSP1 had a closer relationship with bacterial phage T7 than other cyanophages. In conclusion, we successfully utilized cryo-EM SPA to reveal the assembling, DNA gating, and evolutionary mechanisms of the cyanophage P-SCSP1.