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J. Virol., 04 1995, 2271-2278, Vol 69, No. 4
Z Wu, SC Kayman, W Honnen, K Revesz, H Chen, S Vijh-Warrier, SA Tilley, J McKeating, C Shotton and A Pinter
A number of monoclonal antibodies (MAbs) with various levels of
neutralizing activity that recognize epitopes in the V1/V2 domain of
LAI-related gp120s have been described. These include rodent antibodies
directed against linear and conformational epitopes and a chimpanzee MAb,
C108G, with extremely potent neutralizing activity directed against a
glycan-dependent epitope. A fusion glycoprotein expression system that
expressed the isolated V1/V2 domain of gp120 in native form was used to
analyze the structural characteristics of these epitopes. A number of MAbs
(C108G, G3-4, 684-238, SC258, 11/68b, 38/66a, 38/66c, 38/62c, and CRA3)
that did not bind with high affinity to peptides immunoprecipitated a
fusion glycoprotein expressing the V1/V2 domain of HXB2 gp120 in the
absence of other human immunodeficiency virus sequences, establishing that
their epitopes were fully specified within this region. Biochemical
analyses indicated that in the majority of V1/V2 fusion molecules only five
of the six glycosylation signals in the V1/V2 domain were utilized, and the
glycoforms were found to be differentially recognized by particular MAbs.
Both C108G and MAbs directed against conformational epitopes reacted with
large fractions of the fully glycosylated molecules but with only small
fractions of the incompletely glycosylated molecules. Mutational analysis
of the V1 and V2 glycosylation signals indicated that in most cases the
unutilized site was located either at position 156 or at position 160,
suggesting the occurrence of competition for glycan addition at these
neighboring positions. Mutation of glycosylation site 160 destroyed the
C108G epitope but increased the fraction of the molecules that presented
the conformational epitopes, while mutation of the highly conserved
glycosylation site at position 156 greatly diminished the expression of the
conformational epitopes and increased expression of the C108G epitope.
Similar heterogeneity in glycosylation was also observed when the HXB2
V1/V2 fusion glycoprotein was expressed without most of the gp70 carrier
protein, and thus, this appeared to be an intrinsic property of the V1/V2
domain. Heterogeneity in expression of conformational and glycan-dependent
epitopes was also observed for the natural viral env precursor, gPr160, but
not for gp120. These results suggested that the closely spaced
glycosylation sites 156 and 160 are often alternatively utilized and that
the pattern of glycosylation at these positions affects the formation of
the conformational structures needed for both expression of native epitopes
in this region and processing of gPr160 to mature env products.
Copyright © 1995, American Society for Microbiology
Characterization of neutralization epitopes in the V2 region of human immunodeficiency virus type 1 gp120: role of glycosylation in the correct folding of the V1/V2 domain
Public Health Research Institute, New York, New York 10016.
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