pentons

Pentons are the pentameric protein complexes that occupy the vertices of the adenovirus capsid. The term is commonly used to refer to the combination of the penton base and the associated fiber protein at each vertex of the icosahedral particle. Collectively, there are 12 penton complexes on an intact virion.

The penton base forms a five-subunit core that anchors the fiber spike to the capsid. A trimeric fiber protrudes from the penton base, with the distal knob responsible for receptor binding. The penton base itself contains an integrin-binding loop, often featuring an RGD motif, which facilitates interactions with host cell integrins.

During entry, the fiber knob first engages a primary receptor such as the coxsackievirus and adenovirus receptor (CAR) depending on serotype, positioning the virion at the cell surface. The penton base's integrin interactions trigger internalization via endocytosis and subsequent trafficking to endosomes, contributing to viral uptake and disassembly.

In research and clinical vector design, pentons are of interest because modifications to the penton base or fiber can alter cell tropism, immune recognition, and transduction efficiency. Adenovirus vectors used in gene therapy and vaccines often incorporate altered penton or fiber components to improve safety and targeting. Structural studies using cryo-electron microscopy and X-ray crystallography have characterized the arrangement and interfaces of penton complexes within the capsid.

The term penton derives from pent- meaning five and on from Greek -on. In virology, pentons commonly refer to these vertex-associated protein complexes, though usage may vary by source.