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Figure 2.
Figure 2 Conformational rearrangement of protein E. Comparison
of the overall organization of the protein in the neutral- and
acid-pH forms. The 'top' and 'side' views are indicated in the
top and bottom rows, respectively. The three domains of sE are
labeled dI, dII, and dIII. The color coding is defined in the
legend to Figure 1. (A) Neutral -pH, dimeric conformation of sE
in a surface representation. The carbohydrate residues (labeled
CHO) are indicated in pink. A ribbon diagram is intercalated
between the top and side views, at the same scale and
orientation as the foreground subunit in the side view. Several
 -sheets
that are referred to in the text are indicated (i.e., the top
and bottom -sheets
of dI, the klD[0] and gfeah sheets of dII). In the ribbon
diagram, the arrows representing the -strands
in the bottom sheet of dI are white. The last amino acid
observed in the crystal structure (K395; Rey et al, 1995) is
indicated by an open blue star, labeled C-term. The lipid
bilayer is diagrammed at the same scale underneath the dimer in
the side view, with the aliphatic region in pale yellow and the
lipid head regions in gray. (B) Low-pH conformation of sE. As in
panel A, only one subunit is colored and the others are shown in
white and gray. The arrows show the dimensions of the molecule,
including all atoms with a Van der Waals radius of 2 Å. In the
side view, the purple region indicates the dIII/stem linker,
which ends at the last amino acid visible in the electron
density map (R401) indicated by an open red star (labeled
C-ter). Note the vertical groove that follows the C-terminus
along the interface between neighboring dIIs in the trimer. The
lipid bilayer is diagrammed as in (A), indicating the postulated
interaction of the fusion peptide loops with the lipid heads.
(C) Ribbon diagram of the polypeptide chain of sE in the
trimeric conformation. In the top view, note the extended
conformation of the dI/dIII linker (purple). In the side view,
only the colored subunit displayed in (B) is shown for clarity.
The disordered segments (the E[0]F[0] loop in dI and the fg loop
in dII) are indicated by broken lines and labeled. The
C-terminus is indicated as in (B). It shows that the predicted
 -helix
H1 of the stem would interact with the two short helices of dII.
(D) Conformational rearrangement of sE. dI of the sE subunit in
the conformation observed in the dimer (Figure 1A) was
superposed on dI of the colored subunit in the trimer shown in
(C), as explained in the text. Curved gray arrows show the
movement of the domains to reach the conformation indicated in
(C). In the side view, the two -sheets
of dII that change their relative orientation are labeled
(klD[0] and gfeah).
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