Cryo-electron microscopy studies of empty capsids of human parvovirus B19 complexed with its cellular receptor.

Abstract

The three-dimensional structures of human parvovirus B19 VP2 capsids, alone and complexed with its cellular receptor, globoside, have been determined to 26 A resolution. The B19 capsid structure, reconstructed from cryo-electron micrographs of vitrified specimens, has depressions on the icosahedral 2-fold and 3-fold axes, as well as a canyon-like region around the 5-fold axes. Similar results had previously been found in an 8 A resolution map derived from x-ray diffraction data. Other parvoviral structures have a cylindrical channel along the 5-fold icosahedral axes, whereas density covers the 5-fold axes in B19. The glycolipid receptor molecules bind into the depressions on the 3-fold axes of the B19:globoside complex. A model of the tetrasaccharide component ofgloboside, organized as a trimeric fiber, fits well into the difference density representing the globoside receptor. Escape mutations to neutralizing antibodies map onto the capsid surface at regions immediately surrounding the globoside attachment sites. The proximity of the antigenic epitopes to the receptor site suggests that neutralization of virus infectivity is caused by preventing attachment of viruses to cells.Parvovirus B19 is the only member of Parvoviridae pathogenic to man (1, 2). Acute infection causes a childhood measles-like rash condition, erythrema infectosium, also known as fifth disease, and acute or chronic arthritis in adults. In persons with underlying hemolysis, acute B19 infection results in transient aplastic crises, due to cessation in red blood cell production, which is caused by tropism of B19 to erythroid progenitor cells. In immunocompromised individuals, such as AIDS patients and patients undergoing immunosuppressive drug therapy, persistent B19 infection causes chronic severe anemia due to erythroid marrow failure. B19 infection of pregnant women may cause hydrops fetalis (congestive heart failure) of the fetus and spontaneous abortions due to the inability of the fetus to mount an adequate immune response.Parvoviruses have a single-stranded DNA genome encapsidated in a T = 1 (60 structurally equivalent subunits) icosahedral protein capsid, approximately 260 A in diameter.The major structural protein, VP2, has a molecular mass of 58,000 and consists of an eight-stranded, anti-parallel, (3-barrel motif (with , strands B, C, . . . , I), similar to that found in many other viral capsid proteins (3). This (3-barrel structure contains only about one-third of the amino acid content in each polypeptide and lies mostly below the capsid surface, which is formed by large insertions between the /3-strands. For canine parvovirus (CPV) (4) and feline panleukopenia virus (FPV) (5), the loops between the B and C (loop 1), E and F (loop 2), and G and H (loops 3 and 4) (3-strands contain 36, 74, and 223 residues, respectively. These loops form most of the capsid surface, with loops 3 and 4 forming the bulk of the spikes that extend 22 A radially outwards around the 3-fold axes. The insertion of 20 amino acids between the D and E st...

Genetic modifications of the adeno-associated virus type 2 capsid reduce the affinity and the neutralizing effects of human serum antibodies

“…19 These data indicate the importance of the threefold-proximal peak region in the recognition by the humoral immune response, as it has been already shown for B19 or CPV. [29][30][31] It remains to be elucidated whether these mutations interfere with Ab binding directly or indirectly due to structural changes in adjacent regions.…”

“…29,30,31,[36][37][38] At the beginning of our studies the capsid structure of AAV was still unknown. Alignments of these related parvoviruses with AAV led to hypothetical models of the AAV capsid, and systematic mutagenesis helped to map functional sites on the capsid.…”

“…30 Similarly, the epitopes of two monoclonal neutralizing Ab of B19 parvovirus have also been mapped to the threefold spike region. 31 Therefore, it is possible that immunogenic sites of AAV are also located in variable regions of the threefold spike region.…”

AAV Hybrid Serotypes: Improved Vectors for Gene Delivery

“…The first few parvovirus capsid structures to be solved were the canine parvovirus [Tsao, J et al, 1991], followed by feline panleukopenia virus [Agbandje, M et al, 1993], B19 [Chipman, PR et al, 1996;Kaufmann, B et al, 2004], the minute virus of mice (MVM) [Llamas-Saiz, AL, 1997] and Galleria mellonella densovirus [Simpson, AA et al, 1998]. The structural details from these parvovirus capsids have been used as a foundation for many AAV studies because of their structural similarity in several domains.…”

Human Parvovirus B19 VP2 Empty Capsids Bind to Human Villous Trophoblast Cells in vitro Via the Globoside Receptor

“…-labeling of B19 VP2 empty capsids B19 VP2 empty capsids were visualized before iodination, using transmission electron microscopy (Center for Biologic Imaging, University of Pittsburgh, PA) to confirm their predicted icosahedral shape and size (18-24 nm) expected for intact assembled B19 virions 1,9 . These selfassembled, non-infectious B19 VP2 empty capsids were generated using a baculovirus expression vector (Biotrin International).…”