Structure of adeno-associated virus-2 in complex with neutralizing monoclonal antibody A20

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...

“…6A and B). Residues in the 2/5-fold wall have been reported to play a role in AMDV tissue tropism and pathogenicity (48,64) as well as in antibody reactivity to AAV2 (65).…”

Section: Resultsmentioning

confidence: 99%

“…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

“…This change is detected by antibodies A20 and C37 (24,25) showing a stronger reaction with VPs sedimenting in the range of 6.5S to 11S when AAP was coexpressed than when VP3 was expressed alone. It may also be the case that the A20 reaction reflects only subunit oligomerization necessary to build up the A20 epitope (14). The decrease in the reaction with antibody B1 in fractions with low S values under nondenaturing conditions may indicate a competition between AAP and the binding of MAb B1 to VP3 (Fig.…”

Section: Discussionmentioning

confidence: 99%

Properties of the Adeno-Associated Virus Assembly-Activating Protein

Naumer

Sonntag

Schmidt

et al. 2012

b Adeno-associated virus (AAV) capsid assembly requires expression of the assembly-activating protein (AAP) together with capsid proteins VP1, VP2, and VP3. AAP is encoded by an alternative open reading frame of the cap gene. Sequence analysis and site-directed mutagenesis revealed that AAP contains two hydrophobic domains in the N-terminal part of the molecule that are essential for its assembly-promoting activity. Mutation of these sequences reduced the interaction of AAP with the capsid proteins. Deletions and a point mutation in the capsid protein C terminus also abolished capsid assembly and strongly reduced the interaction with AAP. Interpretation of these observations on a structural basis suggests an interaction of AAP with the VP C terminus, which forms the capsid protein interface at the 2-fold symmetry axis. This interpretation is supported by a decrease in the interaction of monoclonal antibody B1 with VP3 under nondenaturing conditions in the presence of AAP, indicative of steric hindrance of B1 binding to its C-terminal epitope by AAP. In addition, AAP forms high-molecular-weight oligomers and changes the conformation of nonassembled VP molecules as detected by conformation-sensitive monoclonal antibodies A20 and C37. Combined, these observations suggest a possible scaffolding activity of AAP in the AAV capsid assembly reaction.A deno-associated virus (AAV) is a nonenveloped singlestranded DNA virus of the Parvoviridae family (15). To date, 13 distinct human or nonhuman primate AAV serotypes have been described and numerous recombinant species have been isolated (10). The AAV assembly pathway proposed by Myers and Carter suggests the rapid formation of empty capsids into which the single-stranded genome is inserted in a slow reaction (16). While the process of genome replication has been elucidated in great detail (15,22), molecular events underlying capsid formation and genome encapsidation are less well understood (12).Capsid assembly occurs in the nuclei of infected cells, where capsids are first detectable in the nucleoli but are spread throughout the nucleus at later stages of infection (23). Expression of the cap gene is sufficient for capsid formation. Besides the three capsid proteins, VP1, VP2, and VP3, known to be expressed from open reading frame 1 (ORF1), the cap gene encodes an assembly factor, the assembly-activating protein (AAP), from a second ORF, ORF2 (21). AAP is essential for capsid assembly. It targets newly synthesized capsid proteins to the nucleolus and promotes capsid formation in a still unknown way. AAPs of some, but not all, AAV serotypes can cross-complement each other in the assembly reaction (20). AAP is a rather unstable protein but becomes stabilized upon the coexpression of capsid protein VP3. However, this stabilizing effect depends very much on the serotype of the coexpressed capsid protein, indicating specific AAP-VP protein interactions (20). AAP amino acid sequence alignment of serotypes 1 to 13 shows a high degree of homology. Only AAPs from serotypes 4, 5, 1...

“…The surface expo- sure of these residues was also predicted based on a model by Arbetman et al (13). The surface-localized residues occupy analogous regions to those mapped as antigenic footprints on other AAV capsids, for example, AAV2 and AAV8 (97,100,101,114), and thus likely dictate the antigenic differences reported between the two viruses when their transduction efficiencies were compared in the presence of intravenous immunoglobulin (13). Internal capsid volumes are comparable between AAV2, AAV4, and AAV5 and do not support an increased packaging capacity for AAV5 compared to other AAVs.…”

Section: Fig 2 Aav Capsid Surfaces (A Cmentioning

confidence: 98%

Structural Insights into Adeno-Associated Virus Serotype 5

Govindasamy

DiMattia

Gurda

et al. 2013

The adeno-associated viruses (AAVs) display differential cell binding, transduction, and antigenic characteristics specified by their capsid viral protein (VP) composition. Toward structure-function annotation, the crystal structure of AAV5, one of the most sequence diverse AAV serotypes, was determined to 3.45-Å resolution. The AAV5 VP and capsid conserve topological features previously described for other AAVs but uniquely differ in the surface-exposed HI loop between ␤H and ␤I of the core ␤-barrel motif and have pronounced conformational differences in two of the AAV surface variable regions (VRs), VR-IV and VR-VII. The HI loop is structurally conserved in other AAVs despite amino acid differences but is smaller in AAV5 due to an amino acid deletion. This HI loop is adjacent to VR-VII, which is largest in AAV5. The VR-IV, which forms the larger outermost finger-like loop contributing to the protrusions surrounding the icosahedral 3-fold axes of the AAVs, is shorter in AAV5, creating a smoother capsid surface topology. The HI loop plays a role in AAV capsid assembly and genome packaging, and VR-IV and VR-VII are associated with transduction and antigenic differences, respectively, between the AAVs. A comparison of interior capsid surface charge and volume of AAV5 to AAV2 and AAV4 showed a higher propensity of acidic residues but similar volumes, consistent with comparable DNA packaging capacities. This structure provided a three-dimensional (3D) template for functional annotation of the AAV5 capsid with respect to regions that confer assembly efficiency, dictate cellular transduction phenotypes, and control antigenicity. R ecombinant adeno-associated viruses (rAAVs) are promising viral vectors for gene delivery applications (1, 2). These viruses belong to the single-stranded DNA (ssDNA)-packaging Parvoviridae and genus Dependovirus. Hundreds of AAV genotypes have been sequenced from several mammalian species, and to date 12 serotypes (AAV1 to AAV12) have been defined for the human and nonhuman primate isolates (3-15). The 12 serotypes are classified into eight genetic groups, clades A to F and clonal isolates AAV4 and AAV5, based on antigenic reactivity and sequence similarity (15). The groups are represented by AAV1 to AAV9, with AAV1 and AAV6 belonging to the same clade A because of their high sequence similarity and antigenic cross-reactivity. The representative members share ϳ55 to 99% sequence identity, with AAV4 and AAV5 being the most divergent from each other and from the other members.The linear ssDNA AAV genome, ϳ4.7 kb in length, contains two genes: cap, which encodes the capsid viral proteins (VPs; VP1, ϳ87 kDa; VP2, ϳ73 kDa; VP3, ϳ62 kDa) and rep, which encodes the replication proteins necessary for genome replication and genome packaging. Inverted terminal repeats (ITRs) at the end of the AAV genome, 145 bp in length, are the only essential active sequence required to function as (i) the origin for DNA replication, (ii) the packaging signal, and (iii) integration sites (16)(17)(18)(19). Recombina...