Structure and assembly mechanism of virus-associated pyramids.

Viruses have developed intricate molecular machines to infect, replicate within and escape from their host cells. Perhaps one of the most intriguing of these mechanisms is the pyramidal egress structure that has evolved in archaeal viruses, such as SIRV2 or STIV1. The structure and mechanism of these virus-associated pyramids (VAPs) has been studied by cryo-electron tomography and complementary biochemical techniques, revealing that VAPs are formed by multiple copies of a virus-encoded 10-kDa protein (PVAP) that integrate into the cell membrane and assemble into hollow, sevenfold symmetric pyramids. In this process, growing VAPs puncture the protective surface layer and ultimately open to release newly replicated viral particles into the surrounding medium. PVAP has the striking capability to spontaneously integrate and self-assemble into VAPs in biological membranes of the archaea, bacteria and eukaryotes. This renders the VAP a universal membrane remodelling system. In this review, we provide an overview of the VAP structure and assembly mechanism and discuss the possible use of VAPs in nano-biotechnology.