Arch Virol (2000) 145: 2087–2103
A single point mutation in HIV-1 V3 loop alters
the immunogenic properties of rgp120
, G. A. Pestano
, J. Riley
, A. S. Hasan
, M. Pezzano
, M. Samms
K. J. Park
, J. Guyden
, and W. M. O. Boto
Department of Biology, The City College of New York, New York, U.S.A.
Biology Doctoral Program, The City University of New York, New York, U.S.A.
Department of Cancer Immunology and AIDS, Dana-Farber Cancer Institute,
Harvard Medical School, Boston, Massachusetts, U.S.A.
Biochemistry Doctoral Program, The City University of New York, New York, U.S.A.
Accepted May 3, 2000
Summary. The results of the study presented in this report show that clones of env
derived from genetically divergent HIV-1 ﬁeld isolates fall into two major subsets
based on the predicted secondary structure of the V3 region in gp120. One sub-
set exempliﬁed by the clones A-UG06c, B-RT3.12 and C-UG045 is predicted to
assume a ␤-turn conformation in the V3 loop and comprises the GPGX
The other subset exempliﬁed by the clones D-UG23c and D-UG042 (GX
deﬁcient in the expression of the ␤-turn in the loop. Since secondary conforma-
tions are highly likely to confer antigenic properties in a protein backbone at least
for B cells, we have used nucleic acid immunization to test the effect of the ␤-turn
deﬁciency on the immunogenic potential of rgp120 encoded in these ﬁeld isolates.
As hypothesized, inoculation of BALB/c mice with the env plasmid encoding the
␤-turn expressing rgp120 molecules resulted in the development of a vigorous
antibody response to the homologous V3 loop peptides. In contrast, immunization
with an rgp120 clone deﬁcient in the ␤-turn in the V3 loop showed no evidence
of antibody development to the V3 loop. Instead, the latter clones triggered T
cell proliferative responses and markedly increased the level of IL-2 and IFN-␥
production by T cells. Signiﬁcantly, reconstitution of the ␤-turn conformation by
site-directed mutagenesis of a single V3 loop residue yielded rgp120 molecules
which restored antibody production while diminishing the cell-mediated immune
(CMI) responses to the V3 residue. These observations demonstrate the marked
impact of a single amino acid substitution on the immunogenic properties of V3
region in gp120 encoded by divergent HIV-1 ﬁeld isolates.