Capsomeren

Capsomeren are the protein subunits that assemble to form the capsid, the protective protein shell that surrounds a virus’s genome. Each capsomeren is composed of one or more capsid proteins and can self-assemble into higher‑order structures in the absence of nucleic acid, although genome packaging can influence final geometry.

In many icosahedral viruses, capsomeren occur as pentameric units (five subunits) and hexameric units (six subunits). Twelve pentameric capsomeren and multiple hexameric capsomeren arrange according to icosahedral symmetry, described by the triangulation number T, to form a closed shell.

Capsomeren assembly is driven by protein–protein interactions and, in some viruses, by scaffolding proteins or chaperones. The assembly process often proceeds in a stepwise fashion during virion maturation, and the resulting capsid provides mechanical stability and protects the genome against environmental stresses and host defenses.

Some viruses employ non‑icosahedral or complex capsids in which capsomeren organization deviates from the classic pentamer/hexamer pattern; bacteriophages and large DNA viruses show a variety of architectures.

Understanding capsomeren and their interfaces is important for antiviral strategies that disrupt capsid assembly and for bioengineering applications that use virus‑like particles as nanomaterials.