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J Virol, May 1998, p. 4396-4402, Vol. 72, No. 5
0022-538X/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Structure of a Neutralizing Antibody Bound
Monovalently to Human Rhinovirus 2
Elizabeth A.
Hewat,1,*
Thomas C.
Marlovits,2 and
Dieter
Blaas2
Institut de Biologie Structurale Jean-Pierre
Ebel, 38027 Grenoble, France,1 and
Institute of Biochemistry, University of Vienna, A-1030
Vienna, Austria2
Received 9 July 1997/Accepted 26 January 1998
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ABSTRACT |
The structure of a complex between human rhinovirus 2 (HRV2) and
the Fab fragment of neutralizing monoclonal antibody (MAb) 3B10 has
been determined to 25-Å resolution by cryoelectron microscopy and
three-dimensional reconstruction techniques. The footprint of 3B10 on
HRV2 is very similar to that of neutralizing MAb 8F5, which binds
bivalently across the icosahedral twofold axis. However, the 3B10 Fab
fragment (Fab-3B10) is bound in an orientation, inclined at
approximately 45° to the surface of the virus capsid, which is
compatible only with monovalent binding of the antibody. The canyon
around the fivefold axis is not directly obstructed by the bound Fab.
The X-ray structures of a closely related HRV (HRV1A) and a Fab
fragment were fitted to the density maps of the HRV2-Fab-3B10 complex
obtained by cryoelectron microscope techniques. The footprint of 3B10
on the viral surface is largely on VP2 but also covers the VP3 loop
centered on residue 3064 and the VP1 loop centered on residue 1267. MAb
3B10 can interact directly with VP2 residue 2164, the site of an escape
mutation on VP2, and with VP1 residues 1264 to 1267, the site of a
deletion escape mutation. Deletion of these residues shortens the VP1
loop, moving it away from the MAb binding site. All structural and
biochemical evidence indicates that MAb 3B10 binds to a conformation
epitope on HRV2.
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TEXT |
Picornaviruses are small
single-stranded RNA viruses, 300 Å in diameter, some of which exhibit
great antigenic variation (26). Human rhinoviruses, (HRVs),
medically important members of the picornavirus family, are the major
cause of the common cold. Their capsid is composed of 60 copies each of
four viral coat proteins, VP1, VP2, VP3, and VP4, on a T=1 icosahedral
lattice (25). The HRVs are classified into a major group and
a minor group based on their specificities for cell receptors:
intercellular adhesion molecule 1 for the major group (see, for
example, reference 11) and members of the
low-density lipoprotein receptor family for the minor group
(15). The structures of several HRVs representing both
groups are known (e.g., HRV14 [25], HRV1A
[16], HRV16 [12, 21], and HRV3
[39]). The study of escape mutants to neutralization
by monoclonal antibodies (MAbs) has led to the definition of four
neutralizing immunogenic (NIm) sites (IA, IB, II, and III) for the
major-group virus HRV14 (29) and three such sites (A, B, and
C) for the minor-group virus HRV2 (1). Reviews of
picornavirus antigenicity and its relation to virus structure are found
in references 6 and 18,
respectively.
Antibodies play an important role in combating viral infection, and a
number of mechanisms for antibody-mediated neutralization of viruses
have been proposed. It is possible that each antibody is capable of
invoking more than one mechanism; however, the relative importance of
these mechanisms in vitro, and more importantly in vivo, remains
uncertain. The proposed mechanisms include viral aggregation as a
result of the interlinking of particles (3), inhibition of
virus receptor binding, and inhibition of virus uncoating
(20). Antibodies also mark invading particles for destruction by the complement or other pathways of the immune system.
Viral aggregation and inhibition of receptor binding can be detected
biochemically in vitro and have been shown to occur for selected
neutralizing MAbs. Observations of large pI changes upon antibody
binding have led to the hypothesis that antibody-mediated modification
of the virus capsid may be involved (8); however, the lack
of correlation between pI change and neutralizing strength (4) and the absence of any change in the structure of HRV14 upon binding of a strongly neutralizing MAb, as seen in the X-ray structure of the HRV14-Fab complex (33), argue against
neutralization induced by capsid modification upon antibody binding. In
the crystallographic structures of Fabs complexed with peptides that
mimic the viral epitope for a poliovirus (38) and HRV2
(13, 36), the conformation of the peptide differs from its
homolog on the virus. Taken at face value, these results imply that
antibody binding induces change in capsid conformation (38);
however, since the inherent flexibility of a short peptide allows it to
adopt different conformations to suit its environment, further
confirmation is required. At present there is insufficient information
to say to what extent modification of the virus capsid plays a role in
antibody-induced virus neutralization.
A precise knowledge of the molecular details of virus-antibody
interactions should contribute to our understanding of the mechanisms
of antibody-mediated neutralization. The study of such large molecular
complexes is not always feasible by X-ray crystallography alone;
however, a combination of data from cryoelectron microscopy and X-ray
crystallography is currently proving very fruitful: the picornaviruses,
namely HRVs (e.g., HRV14 [31-33]; HRV2
[13], and foot-and-mouth disease virus [FMDV]
[14]), are receiving particular attention. The
structural study of a selected range of antibodies with different
neutralization characteristics and NIm sites is a step toward
understanding antibody-mediated virus neutralization. In this paper, we
describe structural studies of the complex of the minor-group HRV2 and
neutralizing MAb 3B10 directed against the NIm B site. We employed
cryoelectron microscopy and three-dimensional reconstruction techniques
combined with X-ray crystallographic data. The X-ray structures of the
closely related HRV1A (16), which has 73% amino acid
sequence similarity in its capsid proteins, and a Fab fragment were
fitted to the density maps of the HRV2-Fab-3B10 complex obtained by
cryoelectron microscope techniques. The atomic structure of HRV2,
predicted by comparison with the known HRV1A structure, was also placed in the cryoelectron microscopy density map. The structure of
neutralizing MAb 8F5 bound bivalently to NIm site B of HRV2
(13) is compared with that of MAb 3B10, which binds
monovalently to the same NIm site.
Preparation and purification of HRV2, MAb 3B10, and Fab-3B10.
HRV2 was prepared essentially as described by Skern et al.
(30) with the modifications detailed by Hewat and Blaas
(13). MAb 3B10 was purified from tissue culture supernatants
of hybridomas grown in roller bottles in RPMI containing 5%
immunoglobulin-free serum (Gibco-BRL) by standard methods involving
polyethylene glycol precipitation and ion-exchange chromatography. Fab
fragments were prepared by cleavage with papain followed by Mono-Q
column chromatography. MAb 3B10 was raised against the native HRV2
virus particle.
Neutralization experiments.
Five hundred 50% tissue culture
infectious doses (TCID50) of HRV2 were incubated for 1 h in 100 µl of purified antibodies at the final concentrations
indicated in Fig. 4. The solutions were then transferred to 96-well
plates with subconfluent HeLa-OHIO cells (Flow Laboratories).
Incubation was at 35°C for 3 days, whereupon cells were stained with
amido black and washed with phosphate-buffered saline. The stain
was solubilized in 1 M NaOH, and the A530
was determined for each well with a microplate reader.
Preparation of HRV2-3B10 complexes.
Complexes were prepared as
described previously (13). HRV2 (25 µg) and Fab-3B10 were
incubated at a molar ratio of 1:400 in 50 µl of incubation buffer (50 mM Tris-HCl, 150 mM NaCl, 2 mM CaCl2, 30 mM
MgCl2 [pH 7.4]) for 1 h at room temperature. Excess Fab was removed by passage through an exclusion column (Sephacryl S300
Spun; Pharmacia) which had been equilibrated with incubation buffer.
Assuming no loss of HRV2, the complex was estimated to have a total
protein concentration of 1 µg/µl. The HRV2-MAb-3B10 complex was
prepared as described for the HRV2-Fab-3B10 complex but with a molar
ratio of 1:200. Attempts to remove excess MAbs by passage through a
Spun column resulted in loss of the specimen because of aggregation.
Preparation of frozen hydrated specimens.
Frozen hydrated
specimens were prepared on holey carbon grids as described previously
(13). The holey carbon film supported on 400 mesh grids was
not glow discharged before use. Samples of virus suspension (4 µl)
were applied to grids, blotted immediately with filter paper for 1 to
2 s, and rapidly plunged into liquid ethane cooled by nitrogen gas
at 
175°C. Specimens were observed at a temperature of approximately
either 180°C with a Gatan 626-DH Cryoholder or 175°C with an
Oxford CT3500 Cryoholder in a Phillips CM200 operating at 200 kV.
Images were obtained under low-dose conditions (<10e/Å2)
at a nominal magnification of ×27,500 at 1.8 and 2.5 µm underfocus.
Image analysis.
Preliminary selection of defocus pairs of
micrographs, digitalization, and preparation of virus particle images
for analysis were performed as described previously (28).
The pixel size of 12.5 µm on the micrographs corresponds to a nominal
pixel size of 4.5 Å/pixel for the specimen. Images were reinterpolated
to a pixel size of 1.5 times the original so that 128 by 128 files could be used. Further image analysis was performed on a DEC Alpha by
using modified versions of the MRC icosahedral programs supplied by
S. D. Fuller (9, 10). The orientations and origins of each particle were first determined and refined by the method of common
lines (5) for the higher defocus image. All subsequent refinement was performed with model-based programs (2), to determine the particle origin and orientation, and cross-common lines
(Simplex program) to refine these parameters. The three-dimensional reconstructions were made by Fourier Bessel inversion. The
reconstruction of the high defocus image was used as a starting model
for the low defocus image, and several cycles of refinement were
performed. The best reconstruction used 54 particles and included
information to 25-Å resolution. The phase residual went to 90° at 24 Å
1. All inverse eigenvalues were less than 1.0, and
99.8% were less than 0.1. Isosurface representations of the
reconstructed density were visualized by Explorer on a Silicon Graphics
computer.
Fitting the HRV and Fab X-ray structures to the cryoelectron
microscope reconstructed density map.
The cryoelectron microscope
reconstructed density map of the HRV2-Fab-3B10 complex was scaled to
the X-ray data by comparing the HRV capsid density only. The
spherically averaged density within a spherical shell from a radius of
115 to 145 Å was compared by cross-correlation. This gave a pixel size
of 6.3 (± 0.05) Å/pixel. No correction for the effect of the
contrast-transfer function on the cryoelectron microscopy
reconstruction was made. Since the X-ray structure of Fab-3B10 has not
yet been resolved, the structure of another Fab, Fab-SD6
(37), was employed. The criterion for the choice of Fab was
that the elbow angle should be close to 180°, as seen in the
three-dimensional reconstruction of 3B10. The X-ray structure of
Fab-SD6 was then fitted by eye to the electron microscope density by
using program "O" on a Silicon Graphics computer. The new
coordinates of the Fab were output from "O", and all other Fab
fragments were generated by icosahedral symmetry operations. The
structure of HRV2, as predicted by SwissMod with the HRV1A X-ray
structure as a basis, was also placed in the cryoelectron microscopy
density map.
Cryoelectron microscopy of HRV2-MAb-3B10 and HRV2-Fab-3B10
complexes.
Cryoelectron microscope images of HRV2-MAb-3B10
complexes revealed a very high degree of particle aggregation, in
keeping with previous biochemical observations indicating that MAb 3B10 is bound monovalently to HRV2. These large three-dimensional aggregates are not suitable for image analysis. Cryoelectron microscope images of
complexes between the Fab fragment of 3B10 and HRV2 show a homogeneous
population of particles with a knobbly appearance and no appreciable
aggregation (Fig. 1). It may be deduced
from these images that the Fab fragments do not project radially from the capsid surface, in contrast to Fab-SD6 on FMDV, which does project
radially (14). As in the native HRV2 specimen, a small proportion of the capsids were empty and they were also decorated with
Fab fragments. While it has been shown that the aggregation of
virus-monovalent MAb complexes can be practically eliminated (24), we chose to work exclusively on the virus-Fab complex since it facilitates reconstruction to a higher resolution.
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FIG. 1.
Electron micrographs of frozen hydrated HRV2-Fab-3B10
complex at a defocus of 2.5 (A) and 1.8 µm (B). Bar, 1,000 Å.
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Reconstructed density of the HRV2-Fab-3B10 complex.
Analysis
of the orientations of the HRV2-Fab-3B10 complexes seen in images of
untilted specimens revealed a highly preferred orientation along the
fivefold axis. There is apparently a strong interaction of the
complexes with the air-water interface. This does not allow a
reconstruction with isotropic resolution; hence, images of specimens
tilted by 10° were obtained. The three-dimensional reconstruction
made from a zero-tilt image (not shown) was, however, remarkably
similar to that made from a 10°-tilted image (Fig. 2) despite the missing information. Both
reconstructions show HRV2 decorated with 60 bilobed Fab fragments which
are tilted at an angle of approximately 45° to the viral surface. The
major difference between the two reconstructions is the presence of unexpected density linking the Fabs around the threefold axis in the
untilted case. In both reconstructions, the maximum density in the Fab
is lower than in the viral capsid, indicating a Fab occupancy of 70 to
80%.
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FIG. 2.
(A) Stereo view of the isosurface representation of the
reconstructed HRV2-Fab-3B10 complex viewed down a twofold axis. HRV2
is shaded in grey (radius, <160 Å), and Fab-3B10 is shaded in blue
(radius, >160 Å). Three separate Fab fragments are depicted in shades
of magenta. Note that these are identical symmetry-related Fabs. Only
the front half of the virus-Fab complex is shown. (B) Comparison of the
reconstruction of HRV2-Fab-3B10 (blue) and HRV2-MAb 8F5 (yellow)
(13) viewed down a twofold axis. (C and D) Thick sections
from panel B cut parallel to the plane of the page. The density
corresponding to the single-stranded RNA has been set to zero. A
twofold axis, perpendicular to the plane of the page, lies at the
center of each figure. (C) The differences in binding orientations of
3B10 and 8F5 are visible. (D) The footprints of MAbs 3B10 and 8F5
on HRV2 (arrowheads) are very similar. Icosahedral two-, three-, and
fivefold axes are indicated. Bars, 50 Å.
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The known surface topology of HRVs (
13,
31,
32), i.e., a
pentameric dome on each of the icosahedral fivefold axes surrounded
by
the "canyon" with a raised triangular plateau centered on each
of the icosahedral threefold axes, allowed determination of the
hand of
the electron microscope reconstruction. Bound Fab-3B10
does not
obstruct the canyon, which, by analogy with the major-group
viruses,
may contain the receptor binding site. Comparison of
the
three-dimensional reconstructions of the HRV2-MAb 8F5 (
13)
and HRV2-Fab-3B10 complexes (Fig.
2B, C, and D) shows that, to
a very
good first approximation, both MAbs 8F5 and 3B10 bind to
the same
epitope on HRV2 (NIm site B in HRV2, which is equivalent
to NIm site II
of HRV14 [
29]); however, the Fab fragments are
oriented very differently. The Fab fragments of 8F5 project almost
radially from the viral surface, facing each other across the
twofold
axis and giving rise to bivalent binding of the MAb. In
contrast, the
Fab fragments of 3B10 tilt away from the twofold
axis. Even taking into
account the flexibility of the Fab elbow,
it is not possible to join a
3B10-Fab to any of its neighbors.
Thus, MAb 3B10 binds monovalently to
HRV2. In order to transform
the orientation of Fab-8F5 to that of
Fab-3B10, the Fab must be
rotated by approximately 150° about its
long pseudo-twofold axis
and then tilted towards the viral surface by
45°.
In both the HRV2-MAb 8F5 and HRV2-Fab-3B10 reconstructions, the viral
surfaces are similar (Fig.
2B). However the canyon in
the
HRV2-Fab-3B10 reconstruction is slightly deeper (by a few
angstroms
only). We believe this difference is not significant
at 25-Å
resolution. (The receptor binding site on minor-group
viruses is not
known at present; while it is thought to differ
from that of
major-group viruses, it is probably also in the canyon
area
[
7]).
Fit of X-ray structures of a Fab and HRV1A to the cryoelectron
microscope reconstructed density map.
The atomic structure of a
Fab usually fits almost equally well into a medium-resolution density
map in two orientations related by a 180° rotation about the long
(pseudodyad) Fab axis. This ambiguity can generally be lifted by
observing the orientation of the Fab elbow angle. (The Fab elbow angle
is defined as the angle between the two pseudodyad axes relating the
heavy and light chains in the variable and constant modules).
Unfortunately, the elbow angle of Fab-3B10 visible in the reconstructed
maps is too close to 180° to be of use. However, at 25-Å resolution,
the constant domain of the Fab has an asymmetric shape, which allows
the ambiguity to be resolved (Fig. 2).
The X-ray structures of HRV1A and Fab-SD6 fit the reconstructed density
map of the HRV2-Fab-3B10 complex very well (not shown).
The structure
of HRV2 predicted by SwissMod (
22,
23) fits
equally well
(Fig.
3). Although positions of the
important antigenic
loops in this predicted structure cannot be
considered very reliable,
particularly in the hypervariable regions,
they at least have
the correct residues and numbers of residues in
these loops.
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FIG. 3.
(A) Stereo view of the footprint of 3B10 on HRV2.
Residues 2164 (P [in magenta, top left]) and 1264 to 1267 (KIED [in
black, bottom left]) are sites of escape mutations. (Note that the
first digit denotes the viral capsid protein, here VP2 and VP1,
respectively). An icosahedral twofold axis is just above the top of the
figure. (B) View of part of the HRV2 surface indicating the region
shown in panel A. Icosahedral two-, three-, and fivefold axes are
marked. (C) Visual fit of the X-ray crystallographic structure of
Fab-SD6 (37) into the cryoelectron microscope reconstruction
of the HRV2-Fab-3B10 complex. The section shown was chosen to pass
through the two regions of close contact between the Fab fragments. The
C backbones of three Fab fragments are shown in shades
of magenta and correspond to the similarly shaded Fab fragments in Fig.
2A. The side chains of neighboring Fab fragments approach to within 5 Å (arrows). The approximate position of a twofold axis is indicated.
In both panels A and B, the C backbones of one copy of
VP1, VP2, and VP3 of HRV2 (SwissMod prediction) are depicted in blue,
green, and red, respectively. The electron microscope map is displayed
in dark blue.
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The 3B10 footprint is largely on VP2 and includes the immunogenic loop
centered on residue 2153. However, it also covers the
VP3 loop centered
on residue 3064 and the VP1 loop centered on
residue 1267. MAb 3B10 can
interact directly with VP2 residue
2164, the site of an escape mutation
on the VP2 immunogenic loop.
It probably also interacts with VP1
residues 1264 to 1267, the
site of a deletion escape mutation (Fig.
3A
and B; Table
1).
Deletion of residues
1264 to 1267 shortens the VP1 loop, moving
it away from the MAb binding
site.
In contrast to 8F5 (
36), 3B10 does not bind to any viral
protein on Western blots. Amino acid residues other than those
from the
VP2 loop thus contribute to the binding of 3B10. The
existence of an
escape mutant on VP1 also indicates a conformation
epitope. In the
absence of the HRV2 and Fab-3B10 structures at
atomic resolution, a
more detailed analysis of the Fab-3B10-HRV2
interface is not possible.
The neighboring Fab fragments lie very close to one another. The side
chains approach to within 5 Å across the twofold axis
and around the
threefold axis (Fig.
3C). Thus, it is not surprising
that these two
points of near contact are not dissociated at 25-Å
resolution. Whereas
Fab fragments of 3B10 form a complex with
the virus with an occupancy
of about 80%, the Fab-8F5 complex
shows less than 10% occupancy,
indicating that in this case bivalent
binding of 8F5 increases the
avidity (
13). For 3B10, the distance
between the C-terminal
C
of the heavy chains in Fab fragments
on either side of
the twofold axis is 105 Å; it is 52 Å for neighboring
Fab fragments
around the threefold axis. Even taking into account
the flexibility of
the Fab elbow and hinge, the distance between
the heavy-chain carboxy
termini of neighboring Fab fragments is
too great to allow bivalent
binding of MAb 3B10.
Neutralization experiments.
Infection inhibition experiments
showed that complete 3B10 immunoglobulin G (IgG) had a much stronger
inhibition capacity than Fab fragments (Fig.
4). The combination of this low virus concentration (500 TCID50/0.1 ml) with the large molar
excess of antibodies (in the range of 106:1 to
107:1) reflects the in vivo situation. We consider 3B10 to
be a very weakly neutralizing antibody, as defined by Mosser and
colleagues (20). Also, the relatively low occupancy (70 to
80%) of Fab 3B10 measured in the reconstruction indicates low binding
affinity.
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FIG. 4.
Inhibition of virus infection by 3B10 IgG and Fab.
Infection of HeLa cells by HRV2 is inhibited by 3B10 in a
concentration-dependent manner. HeLa cell monolayers in 96-well plates
were challenged with 500 TCID50 of HRV2 in the presence of
antibody at the concentrations indicated. Cells surviving after 3 days
of incubation were stained, and the A530 was
measured in a microplate reader. The A530 of the
intact monolayer (not infected) was set to 100% protection, whereas
the A530 of infected monolayers in the absence
of antibody was set to 0% protection. Error bars represent standard
deviations of the means of 10 experiments carried out in parallel.
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Discussion of the binding of MAb 3B10 on HRV2 and comparison with
other antipicornavirus MAbs.
MAb 3B10 binds monovalently to a
conformation epitope on immunogenic site B (equivalent to NIm site II
on HRV14), and the bound Fab does not obscure the canyon, although it
is possible that the unbound Fab and the Fc fragment do cause some
steric hindrance. The affinity of Fab-3B10 is high enough to allow
formation of complexes with HRV2, with a Fab occupancy of about 80%.
MAb 8F5 binds bivalently to HRV2 on a contiguous epitope at immunogenic
site B, and again the canyon is not obscured. The
affinity of Fab-8F5
for HRV2 is so low that it forms a complex
with only very low Fab
occupancy. MAb 3B10 binds more strongly
and is a more efficient
neutralizer than 8F5, but neither MAb
is a very strong neutralizing
agent. Due to the topology of its
binding site, MAb 8F5 may cause
inhibition of virus uncoating.
While both MAbs 3B10 and 8F5 bind to the same immunogenic site, the
large difference in binding geometry provides an insight
into what
determines monovalent or bivalent binding of a MAb.
These observations
support the idea (
20) that it is not only
the spanning
distance but also the orientation which determines
the nature of
binding. It should be noted, however, that bivalent
binding of a MAb to
a virus can occur in the absence of a twofold
axis. For example,
bivalent binding across a threefold axis was
seen in the case of a
neutralizing MAb bound to a calicivirus
(rabbit hemorrhagic disease
virus) (
35).
Both MAbs 3B10 and 8F5 bind to the NIm B site on HRV2, which does not
overlap the putative receptor binding site; thus, it
is interesting to
compare our results with those for MAbs against
a site which does
overlap the receptor binding site (Table
2).
Smith and colleagues (
17,
31-34) have made extensive studies
of three MAbs directed
against the NIm 1A site of HRV14 with cryoelectron
microscopy and
three-dimensional reconstruction and with X-ray
crystallography. Two of
the MAbs (12-1A and 17-1A, which differ
by only 5 amino acid residues)
bind bivalently and are very strong
neutralizers; the third MAb (1-1A)
binds monovalently and is a
weak neutralizer. MAbs 12-1A and 17-1A bind
strongly to a very
large area epitope, which involves framework
residues of the heavy
chain. It is also relevant to consider the very
strongly neutralizing
MAb SD6, which binds monovalently to the
picornavirus FMDV-C (
14).
SD6 binds to a contiguous epitope
on the long flexible GH loop
of VP1, and its Fab forms a complex with
100% occupancy. Fab-SD6
neutralizes FMDV-C almost as well as IgG-SD6.
What conclusions can be drawn from these six picornavirus-MAb complexes
for which the structures are known? In this rather
limited collection
of MAbs, there are examples of both strongly
and weakly neutralizing
MAbs which (i) obstruct receptor binding
(e.g., 17-1A and 1-1A), (ii)
bind monovalently to the virus (e.g.,
SD6 and 3B10), and (iii) bind
bivalently to the virus (e.g., 17-1A
and 8F5). The three strongly
neutralizing MAbs, 17-1A, 12-1A,
and SD6, each inhibit receptor binding
and bind strongly to the
virus (they each form a virus-Fab complex with
100% occupation,
as seen by three-dimensional reconstruction). Thus,
it appears
that a MAb which binds strongly to the receptor binding site
will
be a strong neutralizer. The cooperativity of bivalent MAb binding
can give an affinity constant of 100- to 1,000-fold higher than
for the
Fab alone; however, bivalent binding is neither necessary
(e.g., SD6)
nor sufficient (e.g., 8F5) to ensure strong neutralization.
It is the
affinity (or avidity) of the antibody which matters.
Modification of
the virus capsid upon antibody binding leading
to inhibition of one or
more steps in the infection cycle has
been evoked, particularly in the
case of polioviruses (
8,
38),
but there is no evidence for
this in any of the six MAbs considered
here; in fact, the X-ray
structure of the HRV14-Fab-17-1A complex
(
33) shows no
modification of the virus structure. MAbs with
high affinity,
irrespective of their mode of binding, will probably
also be the most
effective in vivo in marking the virus for destruction
by other
pathways of the immune system (
19).
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ACKNOWLEDGMENTS |
We thank S. Fuller for supplying his versions of the MRC
icosahedral programs, J.-P. Eynard and F. Metoz for assistance in running the computers, and R. H. Wade for support.
This work was supported in part by the Austrian Science Foundation
(grants P-12269-MOB and P-9999-MOB to D.B.).
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FOOTNOTES |
*
Corresponding author. Mailing address: Institut de
Biologie Structurale Jean-Pierre Ebel, 41 av. des Martyrs, 38027 Grenoble, France. Phone: (33) 4 76 884568. Fax: (33) 4 76 885494. E-mail: HEWAT{at}IBS.FR.
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J Virol, May 1998, p. 4396-4402, Vol. 72, No. 5
0022-538X/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
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