Capsid Antibodies to Different Adeno-Associated Virus Serotypes Bind Common Regions

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bIcosahedral viral capsids are obligated to perform a thermodynamic balancing act. Capsids must be stable enough to protect the genome until a suitable host cell is encountered yet be poised to bind receptor, initiate cell entry, navigate the cellular milieu, and release their genome in the appropriate replication compartment. In this study, serotypes of adeno-associated virus (AAV), AAV1, AAV2, AAV5, and AAV8, were compared with respect to the physical properties of their capsids that influence thermodynamic stability. Thermal stability measurements using differential scanning fluorimetry, differential scanning calorimetry, and electron microscopy showed that capsid melting temperatures differed by more than 20°C between the least and most stable serotypes, AAV2 and AAV5, respectively. Limited proteolysis and peptide mass mapping of intact particles were used to investigate capsid protein dynamics. Active hot spots mapped to the region surrounding the 3-fold axis of symmetry for all serotypes. Cleavages also mapped to the unique region of VP1 which contains a phospholipase domain, indicating transient exposure on the surface of the capsid. Data on the biophysical properties of the different AAV serotypes are important for understanding cellular trafficking and is critical to their production, storage, and use for gene therapy. The distinct differences reported here provide direction for future studies on entry and vector production.

Section: Discussionmentioning

confidence: 67%

Section: Discussionmentioning

confidence: 99%

Comparative Analysis of Adeno-Associated Virus Capsid Stability and Dynamics

Rayaprolu

Kruse

Kant

et al. 2013

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113

100

“…5A and 7). The 3-fold region contains residues important for receptor attachment (in AAV2 and B19) and antibody recognition functions (in AAV2) (21,(65)(66)(67)(68)(69)(70).…”

Section: Resultsmentioning

confidence: 99%

Structure of an Enteric Pathogen, Bovine Parvovirus

Kailasan

Halder

Gurda

et al. 2015

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Bovine parvovirus (BPV), the causative agent of respiratory and gastrointestinal disease in cows, is the type member of the Bocaparvovirus genus of the Parvoviridae family. Toward efforts to obtain a template for the development of vaccines and small-molecule inhibitors for this pathogen, the structure of the BPV capsid, assembled from the major capsid viral protein 2 (VP2), was determined using X-ray crystallography as well as cryo-electron microscopy and three-dimensional image reconstruction (cryoreconstruction) to 3.2-and 8.8-Å resolutions, respectively. The VP2 region ordered in the crystal structure, from residues 39 to 536, conserves the parvoviral eight-stranded jellyroll motif and an ␣A helix. The BPV capsid displays common parvovirus features: a channel at and depressions surrounding the 5-fold axes and protrusions surrounding the 3-fold axes. However, rather than a depression centered at the 2-fold axes, a raised surface loop divides this feature in BPV. Additional observed density in the capsid interior in the cryo-reconstructed map, compared to the crystal structure, is interpreted as 10 additional N-terminal residues, residues 29 to 38, that radially extend the channel under the 5-fold axis, as observed for human bocavirus 1 (HBoV1). Surface loops of various lengths and conformations extend from the core jellyroll motif of VP2. These loops confer the unique surface topology of the BPV capsid, making it strikingly different from HBoV1 as well as the type members of other Parvovirinae genera for which structures have been determined. For the type members, regions structurally analogous to those decorating the BPV capsid surface serve as determinants of receptor recognition, tissue and host tropism, pathogenicity, and antigenicity. IMPORTANCEBovine parvovirus (BPV), identified in the 1960s in diarrheic calves, is the type member of the Bocaparvovirus genus of the nonenveloped, single-stranded DNA (ssDNA) Parvoviridae family. The recent isolation of human bocaparvoviruses from children with severe respiratory and gastrointestinal infections has generated interest in understanding the life cycle and pathogenesis of these emerging viruses. We have determined the high-resolution structure of the BPV capsid assembled from its predominant capsid protein VP2, known to be involved in a myriad of functions during host cell entry, pathogenesis, and antigenicity for other members of the Parvovirinae. Our results show the conservation of the core secondary structural elements and the location of the N-terminal residues for the known bocaparvovirus capsid structures. However, surface loops with high variability in sequence and conformation give BPV a unique capsid surface topology. Similar analogous regions in other Parvovirinae type members are important as determinants of receptor recognition, tissue and host tropism, pathogenicity, and antigenicity. B ovine parvovirus (BPV), the type member of the Bocaparvovirus genus of the Parvoviridae family, was discovered in 1961 in the gastrointestinal tract of di...

“…Nine common AAV variable regions (VRs), VR-I to VR-IX, have been assigned at the apex of the large interstrand loops (28). These VRs contribute to local capsid surface topological differences between the AAV serotypes and contribute to their functional profiles, including receptor attachment, tissue tropism, transduction efficiency, and antigenic reactivity (9,28,30,32,34,(36)(37)(38)(39).…”

mentioning

confidence: 99%

“…Many of the antigenic residues were mapped to the VRs forming the 2/5-fold wall, i.e., VR-I, VR-III, and VR-IX, and the 3-fold protrusions, i.e., VR-IV, VR-V, and VR-VIII, although some residues were buried in the capsid interior (44). More recently, cryo-reconstruction has been used to visualize AAV2 antigenic epitopes for two neutralizing anticapsid monoclonal antibodies (MAbs), A20 (45) and C37-B (36), as well as for antibodies against AAV1, AAV5, AAV6, and AAV8 (36,37). Significantly, these sites were also localized to the 2/5-fold wall and 3-fold protrusions despite a sequence diversity of ϳ60 to 99% between the AAVs, suggesting a commonality in antibody recognition sites.…”

mentioning

confidence: 99%

Adeno-Associated Virus Serotype 1 (AAV1)- and AAV5-Antibody Complex Structures Reveal Evolutionary Commonalities in Parvovirus Antigenic Reactivity

Tseng

Gurda

Chipman

et al. 2015

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110

The clinical utility of the adeno-associated virus (AAV) gene delivery system has been validated by the regulatory approval of an AAV serotype 1 (AAV1) vector for the treatment of lipoprotein lipase deficiency. However, neutralization from preexisting antibodies is detrimental to AAV transduction efficiency. Hence, mapping of AAV antigenic sites and engineering of neutralization-escaping vectors are important for improving clinical efficacy. We report the structures of four AAV-monoclonal antibody fragment complexes, AAV1-ADK1a, AAV1-ADK1b, AAV5-ADK5a, and AAV5-ADK5b, determined by cryo-electron microscopy and image reconstruction to a resolution of ϳ11 to 12 Å. Pseudoatomic modeling mapped the ADK1a epitope to the protrusions surrounding the icosahedral 3-fold axis and the ADK1b and ADK5a epitopes, which overlap, to the wall between depressions at the 2-and 5-fold axes (2/5-fold wall), and the ADK5b epitope spans both the 5-fold axis-facing wall of the 3-fold protrusion and portions of the 2/5-fold wall of the capsid. Combined with the six antigenic sites previously elucidated for different AAV serotypes through structural approaches, including AAV1 and AAV5, this study identified two common AAV epitopes: one on the 3-fold protrusions and one on the 2/5-fold wall. These epitopes coincide with regions with the highest sequence and structure diversity between AAV serotypes and correspond to regions determining receptor recognition and transduction phenotypes. Significantly, these locations overlap the two dominant epitopes reported for autonomous parvoviruses. Thus, rather than the amino acid sequence alone, the antigenic sites of parvoviruses appear to be dictated by structural features evolved to enable specific infectious functions. IMPORTANCEThe adeno-associated viruses (AAVs) are promising vectors for in vivo therapeutic gene delivery, with more than 20 years of intense research now realized in a number of successful human clinical trials that report therapeutic efficacy. However, a large percentage of the population has preexisting AAV capsid antibodies and therefore must be excluded from clinical trials or vector readministration. This report represents our continuing efforts to understand the antigenic structure of the AAVs, specifically, to obtain a picture of "polyclonal" reactivity as is the situation in humans. It describes the structures of four AAV-antibody complexes determined by cryoelectron microscopy and image reconstruction, increasing the number of mapped epitopes to four and three, respectively, for AAV1 and AAV5, two vectors currently in clinical trials. The results presented provide information essential for generating antigenic escape vectors to overcome a critical challenge remaining in the optimization of this highly promising vector delivery system. T he adeno-associated viruses (AAVs), single-stranded DNA packaging viruses belonging to the Parvoviridae family, are promising vectors for gene delivery. There are over 100 AAV genomic isolates, and 13 human and nonhuman serotypes h...