Biology Reference
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mutant virus lacking 301 glycan also demonstrated sensitivity to
CD4i antibodies. In another study, elimination of N-linked glycosyla-
tion in the V1 and V2 loops of pathogenic SIV mac239 rendered the
virus more sensitive to host antibody responses.
169
It is apparent from
the crystal structure that sugar moieties lie proximal to, but not
within, the receptor binding site. Koch and colleagues have per-
formed structure-based deglycosylation of four sites flanking the
receptor-binding region (i.e. 197, 276, 301, and 386). Removal of a
single glycosylation site at the base of V3 loop (i.e. aa 301) has ren-
dered the mutant virus more sensitive to antibody-mediated neutral-
ization by anti-CD4 BS antibodies. Furthermore, deletion of all 4
glycosylation sites has made the resultant virus sensitive to neutraliza-
tion by CD4i antibodies. In an other study, McCaffrey
et al
.
170
have
demonstrated that removal of sugar moieties at positions 293, 299
329, and also 438 and 454 made the SF162 virus more sensitive to
neutralization by CD4BS mAbs and also to V3 loop specific neutral-
izing mAbs. In addition, the deglycosylation of V3 loop (293, 299,
and 329) also made the mutant virus more sensitive to mAbs specific
to CD4i epitope. Furthermore, the same group has also demonstrated
that deglycosylation at positions 293 (V3 loop), 438 (C4 region), and
454 (V5 loop) also rendered the resultant virus more susceptible to
the anti-gp41 mAb 2F5. These studies suggest that carbohydrates at
these positions protect the CD4 binding site, V3 loop, co-receptor
binding site and also gp41 epitope.
170
Further studies will be needed
to evaluate the efficacy of this approach in exposing critical neutraliz-
ing epitopes in Env immunogens.
Hyper-glycosylation for Focusing the Immune
Response Toward Neutralizing Epitopes
Recognized by b12
Burton and colleagues have taken the opposite approach of incorpo-
rating additional carbohydrate residues. They have demonstrated that
four alanine substitutions on the perimeter of the Phe43 cavity of
gp120 reduced the binding of weakly neutralizing CD4 BS antibodies
