Cryoelectron Microscopy Map of Atadenovirus Reveals Cross-Genus Structural Differences from Human Adenovirus

Abstract

A three-dimensional (3D) cryoelectron microscopy reconstruction of the prototype Atadenovirus (OAdV [an ovine adenovirus isolate]) showing information at a 10.6-Å resolution (0.5 Fourier shell correlation) was derived by single-particle analysis. This is the first 3D structure solved for any adenovirus that is not a Mastadenovirus, allowing cross-genus comparisons between structures and the assignment of genus-specific capsid proteins. Viable OAdV mutants that lacked the genus-specific LH3 and p32k proteins in purified virions were also generated. Negatively stained 3D reconstructions of these mutants were used to identify the location of protein LH3 and infer that of p32k within the capsid. The key finding was that LH3 is a critical protein that holds the outer capsid of the virus together. In its absence, the outer viral capsid is unstable. LH3 is located in the same position among the hexon subunits as its protein IX equivalent from mastadenoviruses but sits on top of the hexon trimers, forming prominent "knobs" on the virion surface that visually distinguish OAdV from other known AdVs. Electron density was also assigned to hexon and penton subunits and to proteins IIIa and VIII. There was good correspondence between OAdV density and human AdV hexon structures, which also validated the significant differences that were observed between the penton base protein structures.The Adenoviridae comprise a large family of non-enveloped, icosahedral, generally nonpathogenic viruses with a doublestranded DNA genome (ϳ26.1 to 45 kb) (9). Because of their wide host range, viruses such as human adenovirus type 5 (AdV5) have been developed as gene delivery vectors and applied in the clinic, especially for cancer, monogenic disorders, and vaccination (http://www.wiley.co.uk/genmed /clinical/). While some of these trials have reached phases II and III, there is still considerable room for improvement in vector technology. In particular, there is strong interest in developing vectors that are targeted to specific tissues for improved therapeutic effect (6, 11), and for this purpose, structural information on the virus particle and its constituent molecules is paramount.The family Adenoviridae comprises four genera (Mastadenovirus, Aviadenovirus, Siadenovirus, and Atadenovirus). Of these, the best studied are the mastadenoviruses, which include viruses from numerous mammalian species and all known human AdVs. In contrast, members of the avi-, si-, and atadenoviruses have been isolated from birds, although the latter also occur widely in mammalian and reptilian species (9, 38). The prototype Atadenovirus, an ovine isolate (serotype 7; OAdV), is the only member for which any significant biological studies have been undertaken. OAdV uses a different (unknown) receptor from AdV5 and infects, but does not replicate in, human cells (15). It has also been developed as a gene delivery vector (2) and has regulatory approval to enter a phase I clinical trial for prostate cancer in 2008.Representative genomes from all four genera have now...

Molecular Characterization of a Lizard Adenovirus Reveals the First Atadenovirus with Two Fiber Genes and the First Adenovirus with Either One Short or Three Long Fibers per Penton

“…EM analyses showed the expected morphology for an atadenovirus ( Fig. 2A), with particles 84 Ϯ 6 nm in diameter (n ϭ 50) and an icosahedral but less-faceted shape than HAdV (16).…”

“…Genus-specific genes are mainly located near the ends of the genome, except for mastadenovirus protein V. Minor coat polypeptide IX and core polypeptide V are unique to mastadenoviruses. In atadenovirus virions, the genus-specific structural polypeptides are LH3 and p32K (15,16). Another variable in AdV genome and virion architecture is the number of fiber proteins.…”

Using the E4orf6-Based E3 Ubiquitin Ligase as a Tool To Analyze the Evolution of Adenoviruses

“…Interestingly, and perhaps surprisingly, the LH3 protein has been found in the capsid (52,53) and is simply absent in psittacine adenovirus 3. It is unclear at present if LH3 has an additional role as a nonstructural protein or participates in the ligase complex formed by E4orf6.…”

Novel RecombinantMycobacterium bovisBCG, Ovine Atadenovirus, and Modified Vaccinia Virus Ankara Vaccines Combine To Induce Robust Human Immunodeficiency Virus-Specific CD4 and CD8 T-Cell Responses in Rhesus Macaques

“…While robust anti-HIV-1 T-cell responses were induced by the 4-wk-gap regimen, these might be higher still if more commonly used intervals between individual doses were employed (8,62). Ovine atadenovirus (OAdV) is a novel and underexplored vaccine vector, which is distinct from the more commonly used mastadenoviruses (2,50). Here, we demonstrated that OAdV is capable of antigen presentation for the induction of effective CD8 and CD4 T cell responses in heterologous prime-boost regimens.…”

“…Furthermore, we have formulated HIVA into various vaccine modalities, including plasmid DNA (21), modified vaccinia virus Ankara (MVA) (21), human adenovirus serotype 5 (HAdV-5) (5), Semliki Forest virus replicons (18,49), recombinant lysine auxotroph BCG strain Pasteur (32), and baculovirus-expressed and purified, bluetongue virus-derived chimeric NS1 tubules (37); the immunogenicity of these vectors has been compared directly and in heterologous combinations. More recently, we reported on the immunogenicity of a novel and promising vaccine vector derived from ovine atadenovirus type 7 (OAdV) (5); OAdV is the prototype member of the genus Atadenovirus, which is structurally and biologically distinct from Mastadenovirus (e.g., HAdV-5) (2,50). Importantly, no immunity to OAdV has so far been detected in human sera (26).…”