Characterization of T-even bacteriophage substructures. II. Tail plates

Area of Science:

• Molecular Biology
• Structural Biology
• Virology

Background:

• Bacteriophage T4D tail plates are essential for host cell infection.
• Understanding the structure and composition of tail plates is crucial for deciphering viral assembly and function.

Purpose of the Study:

• To characterize the physical and chemical properties of T4D bacteriophage tail plates.
• To elucidate the subunit composition and structural organization of T4D tail plates.

Main Methods:

• Sedimentation analysis (S(20,w)) to determine conformational changes and dimerization.
• Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) to determine subunit molecular weights.
• Amino acid analysis to compare tail plate composition with other phage components.
• Electron microscopy following dimethyl sulfoxide (DMSO) treatment to visualize substructures.

Main Results:

• Intact T4D tail plates sedimented at 77S within a pH range of 5-9, dimerizing to 124S below pH 5.
• Dissociated tail plates comprised three major proteins (53K, 31K, 17K daltons).
• Amino acid analysis revealed a distinct composition, rich in tryptophan, differing from T4D fibers and tubes.
• DMSO treatment or analysis of mutant lysates revealed tetrad structures, suggesting a composition of nine tetrads per tail plate with six- and threefold symmetry.

Conclusions:

• T4D tail plates possess a stable quaternary structure with distinct protein subunits.
• The tail plate structure exhibits unique properties, including pH-dependent dimerization and susceptibility to DMSO-induced dissociation into tetrads.
• A model proposing nine tetrads forming the T4D tail plate provides a framework for understanding its symmetry and assembly.