What unique features are observed in T = 7 capsid structures of dsDNA viruses?

Sourav PanOctober 28, 2024

Answered

T = 7 capsid structures of dsDNA viruses exhibit several unique features that distinguish them from other viral capsid structures. Here are the key characteristics:

1. Pentamer and Hexamer Arrangement: T = 7 capsids typically consist of 72 pentamers and a varying number of hexamers. In the case of dsDNA viruses, the arrangement of these pentamers and hexamers allows for a complex and stable structure that can accommodate the viral genome.
2. Non-Identical Subunits: Unlike some other viral capsids that rely on a uniform set of identical subunits, T = 7 capsids can incorporate non-identical subunits. For example, in the SV40 capsid, 60 of the pentamers are situated in positions typically occupied by hexamers, demonstrating a unique adaptation of the capsid structure.
3. C-Terminal Arm Flexibility: The C-terminal arms of the capsid proteins in T = 7 dsDNA viruses often exhibit significant flexibility. This flexibility allows the arms to interact with neighboring subunits in a dynamic manner, facilitating the assembly process and contributing to the overall stability of the capsid.
4. Quasi-Symmetry: T = 7 capsids are characterized by quasi-symmetry, which allows for variations in the arrangement of subunits while maintaining a stable and functional structure. This quasi-symmetry is essential for accommodating the structural requirements of the viral genome and ensuring proper assembly.
5. Diverse Protein Interactions: The interactions between the capsid proteins in T = 7 structures can be quite complex, involving both covalent and non-covalent interactions. These interactions help to stabilize the capsid and ensure that it can withstand the pressures of encapsidating the viral genome.
6. Unique Structural Domains: The capsid proteins in T = 7 dsDNA viruses often contain unique structural domains that contribute to their assembly and stability. For example, the presence of β-barrel structures or helix bundles can play a critical role in the overall architecture of the capsid.
7. High Fidelity Assembly: The assembly of T = 7 capsids often involves high-fidelity interactions between subunits, which are crucial for maintaining the integrity of the capsid. This is particularly important for dsDNA viruses, as the capsid must effectively protect the viral genome.
8. Calcium and RNA Binding Sites: In some T = 7 capsids, specific binding sites for calcium ions and RNA are preserved at the interfaces between subunits. These binding sites can play a role in stabilizing the capsid structure and facilitating interactions with the viral genome.
9. Pleomorphic Properties: Some T = 7 capsids exhibit pleomorphic properties, meaning they can adopt multiple shapes or forms. This can be influenced by the local chemical environment and the specific interactions between subunits.