Structure of Adeno-Associated Virus Serotype 5

Abstract

Adeno-associated virus serotype 5 (AAV5) requires sialic acid on host cells to bind and infect. Other parvoviruses, including Aleutian mink disease parvovirus (ADV), canine parvovirus (CPV), minute virus of mice, and bovine parvovirus, also bind sialic acid. Hence, structural homology may explain this functional homology. The amino acids required for CPV sialic acid binding map to a site at the icosahedral twofold axes of the capsid. In contrast to AAV5, AAV2 does not bind sialic acid, but rather binds heparan sulfate proteoglycans at its threefold axes of symmetry. To explore the structure-function relationships among parvoviruses with respect to cell receptor attachment, we determined the structure of AAV5 by cryo-electron microscopy (cryo-EM) and image reconstruction at a resolution of 16 Å. Surface features common to some parvoviruses, namely depressions encircling the fivefold axes and protrusions at or surrounding the threefold axes, are preserved in the AAV5 capsid. However, even though there were some similarities, a comparison of the AAV5 structure with those of ADV and CPV failed to reveal a feature which could account for the sialic acid binding phenotype common to all three viruses. In contrast, the overall surface topologies of AAV5 and AAV2 are similar. A pseudo-atomic model generated for AAV5 based on the crystal structure of AAV2 and constrained by the AAV5 cryo-EM envelope revealed differences only in surface loop regions. Surprisingly, the surface topologies of AAV5 and AAV2 are remarkably similar to that of ADV despite only exhibiting ϳ20% identity in amino acid sequences. Thus, capsid surface features are shared among parvoviruses and may not be unique to their replication phenotypes, i.e., whether they require a helper or are autonomous. Furthermore, specific surface features alone do not explain the variability in carbohydrate requirements for host cell receptor interactions among parvoviruses.

Structural Insights into Adeno-Associated Virus Serotype 5

“…This structure enabled the high-resolution interpretation of amino acid side chains, surface loop regions, and secondary structure elements (Fig. 1B) in contrast to the lowerresolution cryo-electron microscopy and image-reconstructed (cryo-reconstructed) structure and pseudoatomic model previously published for AAV5 (24). Residue 724 is the last C-terminal amino acid.…”

“…Structures determined for AAVs show capsids assembled from the common VP3 region (20)(21)(22)(23)(24)(25)(26)(27)(28)(29). There is currently no experimentally determined structure for VP1u or the overlapping VP1/ VP2 N terminus.…”

Directed evolution of adeno-associated virus to an infectious respiratory virus

“…It is exceedingly difficult to predict which capsid regions should be reengineered to form novel viral-cell interactions that would be optimal to transduce particular tissues, despite advances in understanding AAV structure and function (37)(38)(39)(40). However, the search for AAV variants with novel properties through a variety of algorithms-such as isolating naturally occurring AAV, site-directed mutants, or (most recently) laboratory-evolved variants-has yielded various chimeric AAV viruses with distinct transduction profiles (17,(41)(42)(43)(44).…”

Intracellular trafficking of adeno-associated viral vectors

“…63 Studies focusing on AAV capsid structures have improved since the crystal structure of AAV2 was determined. Efforts to obtain capsid surface details for other AAV serotypes are accelerating 42,85 and have complemented genetic analyses of the AAV2 capsid that has revealed an enormous tolerance for large insertions such as GFP. 86 Such efforts to link sensitive fluorescent protein tags with AAV virions will enhance our capabilities to study AAV trafficking in real time.…”