Evolution of Phage Tail Sheath Protein.

Area of Science:

• Structural biology
• Virology
• Molecular microbiology

Background:

• Sheath proteins are key components of contractile molecular machinery in bacteriophages, contractile injection systems, and bacterial type VI secretion systems (T6SS).
• Despite variations in size and sequence, these sheath proteins exhibit conserved structural features.

Purpose of the Study:

• To model and analyze the structures of 112 contractile phage tail sheath proteins (TShP) from diverse myoviral bacteriophages and archaeal viruses using AlphaFold 2.
• To identify conserved and variable regions within TShPs and elucidate their functional and evolutionary significance.

Main Methods:

• Utilized AlphaFold 2, a machine learning tool, for structural modeling of 112 TShPs.
• Performed structural analysis to identify conserved and variable protein domains.
• Conducted phylogenetic analysis based on structural similarity to infer evolutionary relationships.

Main Results:

• Identified a common core domain in all studied sheath proteins (viral and T6SS), comprising N-terminal and C-terminal regions, essential for tail tube interaction and phage tail assembly.
• Discovered moderately conserved additional domains, potentially acquired during evolution for virion stability or host cell adsorption.
• Proposed evolutionary relationships among TShPs from different viral groups based on structural and phylogenetic analyses.

Conclusions:

• The conserved core of TShPs is fundamental for their role in contractile systems, while variable domains contribute to functional diversification and adaptation.
• Structural modeling and phylogenetic analysis provide insights into the evolution of contractile sheath proteins across different viral lineages and bacterial secretion systems.