Local rules for the self-assembly of a non-quasi-equivalent viral capsid

The structures of many large bacteriophages, such as the P23-77 capsids, do not adhere strictly to the quasi-equivalence principle of viral architecture. Although the general architecture of the P23-77 capsids is classed as T = 28d, it self-assembles from multiple copies of two types of coat protein subunits, and the resulting hexameric capsomers do not conform to the Caspar-Klug paradigm. There are two types of hexamers with distinct internal organization, that are located at specific positions in the capsid. It is an open problem which assembly mechanism can lead to such a complex capsid organization. Here we propose a simple set of local rules that can explain how such non-quasi-equivalent capsid structures can arise as a result of self-assembly.

Automated summary

The structures of many large bacteriophages do not strictly adhere to the quasi-equivalence principle of viral architecture. The P23-77 capsids, classified as T = 28d, self-assemble from multiple copies of two types of coat protein subunits, resulting in hexameric capsomers that do not conform to the Caspar-Klug paradigm. The assembly mechanism that leads to such complex capsid organization remains an open problem.