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Figure 3.
Figure 3. Location of interactions that differ between CR1 and
BoNT/A1 and BoNT/A2 and affect differential BoNT/A binding.
(a) Location of CR1-BoNT/A1 contact residues and residues
differing between BoNT/A1 and BoNT/A2. The alignment of BoNT/A1
and A2 subtypes shows strict sequence conservation in white
letters on red background, and strong sequence conservation in
red letters. The residues composing the CR1 epitope of the H[CN]
lectin (residues 874–1094) and H[CC] trefoil (residues
1095–1295) subdomains are indicated with red triangles,
energetically important residues are shown with black triangles.
Disulfide bonds are indicated using green numbers. The secondary
structure elements of the BoNT/A1 binding domain structure are
labeled  (
-helix),
 (
-strand)
and TT (turn). (b) Structural location of differences between
BoNT/A1 and A2 and impact on CR1 interactions. (i,ii) Surface
representations of BoNT/A1 (yellow) in complex with CR1 (V[L] in
magenta and V[H] in green) showing patches of sequence
variability between BoNT/A1 and BoNT/A2 subtypes in slate blue.
(iii,iv) Close-up view of sequence variability between T1063 and
H0164 of BoNT/A1 (yellow, iii) and modeled P1063 and R0164 of
BoNT/A2 (cyan, iv) in complex with CR1 (V[L] in magenta and V[H]
in green). (v,vi) Surface representations of BoNT/A1 (yellow)
with BoNT/A1 and BoNT/A2 sequence differences in slate blue. Key
differences between BoNT/A1 and BoNT/A2 that are functionally
important for binding (high  G
values) are shown in dark blue (1063 and 1064). Functionally
important BoNT/A residues (high G
values) that do not differ between BoNT/A1 and BoNT/A2 are shown
in red. Panel v shows CR1 with its light and heavy chains in
magenta and green, respectively, with its H1 loop in tan. Panel
vi is looking down onto the CR1 epitope of BoNT/A1 with CR1
removed. (c) Details of the interaction between AR2 and CR1 and
BoNT/A1 and A2 at the H1 loop. Close-up view of the H1 loop
showing sequence and structural differences between BoNT/A1
(yellow) and BoNT/A2 (cyan), in complex with the CR1 (green) and
AR2 (orange) Fabs. The BoNT/A2-CR1 and BoNT/A2-AR2 structures
are modeled.
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