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Anna Stefanik Sobotkova: Structure and Infection Mechanism of Phage CL19

• 0:00 Introduction: Anna Stefanik Sobotkova, a PhD student, presents her research on the structure and infection mechanism of phage CL19.
• 0:19 Phages Defined: Phages are viruses that infect bacteria, coming in various types including filamentous, tailless, and tailed (contractile, long flexible, and short-tailed).
• 0:51 Phage CL19: This specific phage belongs to the short-tailed group and infects Pseudomonas aeruginosa, a significant human pathogen often antibiotic-resistant.
• 1:16 Lytic Cycle: Phage CL19 undergoes a lytic life cycle: attachment to the host, DNA injection, host machinery utilization for replication, new phage assembly, cell lysis, and release of new phages.
• 1:58 Structural Analysis: Cryo-EM and single-particle analysis were used to study the molecular structure of phage CL19, revealing its icosahedral head, tail, and flexible tail fibers.
• 2:22 Icosahedral Capsid: The capsid, containing the phage genome, is composed of major capsid proteins with a highly conserved fold.
• 2:57 Head stabilization: The Fage Head is decorated by head cement and head decoration proteins that stabilize the capsid.
• 3:10 Core Complex: Inside the head, a core complex is composed of cap, middle core, and portal proteins, each with specific roles in the phage life cycle.
• 3:35 Protein Ejection: The cap and middle core proteins are ejected before genome ejection, forming a pore in the host membrane (observed in the related phage T7).
• 4:35 Portal Protein: This protein connects the core protein, phage head, and phage tail.
• 4:43 Tail Structure: The phage tail includes an adapter, hexameric tail nozzle, and long flexible tail fibers (partially resolved). It forms a channel for DNA passage, with "gates" controlling DNA ejection.
• 5:30 Structural Overview: The complete structure of phage CL19 includes the icosahedral head, core complex, and tail proteins.
• 5:41 Early Infection Study Early Infection process was also studied by cryo-electron demography.
• 5:47 Host Surface Structures: P. aeruginosa has flagella (for locomotion) and type IV pili (for surface sensing, attachment, biofilm formation, and phage interaction).
• 6:24 Phage Attachment: The phage likely attaches to the pili via its tail nozzle or tail fibers, then moves closer to the host cell.
• 6:37 Two Potential Mechanisms The mechanism may include diffusion along the P to the cell surface, or Pilus contraction, pulling the phage into proximity.
• 6:52 Cryo-EM Support: Cryo-electron microscopy images show P. aeruginosa with attached phages on the pili.
• 7:23 Infection Mechanism Conclusion: Combining structural and infection data, the proposed mechanism involves phage attachment to type IV pili, penetration of the cell membrane (aided by core protein ejection), and genome ejection into the host cytoplasm.
• 8:12 Acknowledgments: Sobotkova thanks her research group, colleagues, core facilities, and conference organizers.