Characterization of subspecies B1 human adenovirus ORF E3-10.9K

Subspecies B1 human adenoviruses (HAdVs) are important causes of acute respiratory disease in pediatric and military recruit populations. Although extensive epidemiological data document the genetic diversity of these human pathogens, little is known about the relevance of this genetic diversity on the pathogenesis and fitness of subspecies B1 HAdVs. Additionally, the unique molecular biology of these pathogens is understudied compared to the species C HAdV serotypes 2 and 5. One of the uniquely diverse regions of the HAdV genomes is the early region 3 (E3) transcription unit. These genes are implicated in pathogenesis, host-species specificity, and the modulation of the host immune response to infection. Subspecies B1 HAdVs encode a set of novel open reading frames (ORFs) within the E3 region, including E3-20.1K, E3-20.5K, and E3-10.9K. ORF E3-10.9K is highly polymorphic among subspecies B1 HAdVs, and it displays extensive variation among strains of serotypes 3 and 7. In an effort to understand the role ORF E3-10.9K plays in the context of subspecies B1 HAdV infectious cycle and fitness in nature and the biological implications of the observed polymorphism, a biochemical characterization of ORF E3-10.9K-encoded proteins, the investigation of membrane permeabilizing acitivity of these proteins, and the examination of growth phenotypes of virus mutants lacking ORF E3-10.9K was undertaken. This research showed that ORF E3-10.9K was expressed late in infection from the HAdV major late promoter and that its products were N- and O-glycosylated, similar to E3-11.6K/adenovirus death protein (ADP) of species C HAdV. However, ORF E3-10.9K-encoded protein orthologs showed a subcellular localization distinct from the nuclear envelope localization of the E3-11.6K/ADP. Proteins with a hydrophobic domain were capable of permeabilizing membranes in an E. coli expression system, but not in a mammalian expression system. Subspecies B1 HAdV mutants lacking ORF E3-10.9K displayed similar virus growth and egress kinetics as control subspecies B1 HAdVs containing ORF E3-10.9K. These data suggested that ORF E3-10.9K is not the subspecies B1 HAdV equivalent of species C HAdV E3-11.6K/ADP