Abstract
Adenovirus (AdV) capsid organization is considerably complex, not only because of its large size (~950 Å) and triangulation number (pseudo T = 25), but also because it contains four types of minor proteins in specialized locations modulating the quasi-equivalent icosahedral interactions. Up until 2009, only its major components (hexon, penton, and fiber) had separately been described in atomic detail. Their relationships within the virion, and the location of minor coat proteins, were inferred from combining the known crystal structures with increasingly more detailed cryo-electron microscopy (cryoEM) maps. There was no structural information on assembly intermediates. Later on that year, two reports described the structural differences between the mature and immature adenoviral particle, starting to shed light on the different stages of viral assembly, and giving further insights into the roles of core and minor coat proteins during morphogenesis [1,2]. Finally, in 2010, two papers describing the atomic resolution structure of the complete virion appeared [3,4]. These reports represent a veritable tour de force for two structural biology techniques: X-ray crystallography and cryoEM, as this is the largest macromolecular complex solved at high resolution by either of them. In particular, the cryoEM analysis provided an unprecedented clear picture of the complex protein networks shaping the icosahedral shell. Here I review these latest developments in the field of AdV structural studies.
Highlights
AdV Structure: A Historical PerspectiveAdenoviruses [5] have long been of interest in the basic virology field. They are present in most vertebrates [6]
Adenovirus (AdV) capsid organization is considerably complex, because of its large size (~950 Å) and triangulation number, and because it contains four types of minor proteins in specialized locations modulating the quasi-equivalent icosahedral interactions
AdV is the largest complex solved by protein crystallography, and the largest, and one of the few so far, solved at atomic resolution by cryo-electron microscopy (cryoEM) [93]
Summary
Adenoviruses [5] have long been of interest in the basic virology field. They are present in most vertebrates [6]. Even at the limited resolution attained, the difference maps showed for the first time the shape of the penton complex, and the location of outer and inner densities reinforcing the capsid at specific positions These were interpreted with the help of the known copy numbers and molecular weights, and assigned to minor coat proteins IIIa, VI, and IX. The different species and genera differ in some of the minor capsid components, the general virion architecture is conserved This includes particle size, hexon packing, external reinforcement by minor proteins at the 3-fold axes in the GONs, and internal densities beneath the vertices. Information obtained on AdV is likely to apply to a large family of highly complex viruses
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