Morphological adaptations facilitating attachment for archaeal viruses

Abstract

Little is known regarding the attachment and entry process for any archaeal virus. The virus capsid serves multiple biological functions including: to protect the viral genome during transit between host cells, and to facilitate attachment and entry of the viral genome to a new host cell. Virus attachment is conducted without expenditure of stored chemical energy i.e. ATP hydrolysis. Instead, virus particles depend on diffusion for transportation and attachment from one host cell to another. This thesis examines the attachment process for two archaeal viruses. Sulfolobus turreted icosahedral virus (STIV) is well characterized for an archaeal virus. Still, no information is available concerning STIV attachment or entry. The research presented here shows that STIV attaches to a host cell pilus. Furthermore, combining the previously determined atomic model for the virus, with cryo-electron tomography, a pseudo-atomic model of the interaction between the host pilus and virus was determined. Based on this data, a model is proposed for the maturation of the virus capsid from a noninfectious to an infectious form, by dissociation of accessory proteins. Finally, a locus of genes is identified in the host cell, encoding proteins essential for viral infection, that are likely components of the pili structure recognized by STIV. The isolation of a new archaeal virus, Thermoproteus Piliferous Virus 1 (TSPV1), is also presented here. The TSPV1 virion has numerous fibrous extensions from the capsid, of varying length, that are the first observed for any virus. The capsid 2-3nm fibers likely serve to extend the effective surface area of the virus, facilitating attachment to host cells. Characterization of this new virus was conducted, including genome sequencing and determination of the protein identity for the capsid fibers. The research presented here provides a substantial advancement in our knowledge of the attachment process for archaeal viruses. Attachment to host pili is now emerging as a common theme for archaeal viruses. Furthermore, the isolation of the new archaeal virus TSPV1 demonstrates a novel strategy to increase the probability of interaction between a virus and host cell.