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Figure 4.
Figure 4 (A) The LeuAMS binding site showing the major
interacting residues. Hydrogen bonds are shown as dashed green
lines and a tightly bound water as a green sphere. The
catalytically essential class 1 motifs H^49IGH and M^638SKS are
shown in cyan and red, respectively. The side chain of Tyr43 is
omitted for clarity, but is visible in (C). (B) The
conformational changes associated with LeuAMS binding. The view
is the same as in (A). The pink ribbon diagram, pink side chains
and pink labels correspond to the apo-structure (mercury
derivative) and the grey ribbon and yellow side chains belong to
the LeuAMS-bound structure. Upon binding of the adenosine
moiety, the HIGH and MSKS loops towards the active centre,
Gln574 and Glu540 move to bind the ribose tightly, and helices
H18 and H3 refold to permit packing of the ZN-1 domain close to
the active site [see the text and (C)]. A sulfate ion (not
shown) is bound to His49 and His52 in the apo-structure, but not
in the LeuAMS-bound structure. (C) Proximity of Arg178 to the
active center in the LeuAMS complex. Colouring as in (B) with
water molecules as green spheres and the Zn-1 atom as a red
sphere. One of the zinc ligands (His179) and the adenosine
moiety of the LeuAMS are omitted for clarity. The positions of
Leu544 and Leu84 sterically prevent the packing of the ZN-1
domain close to the active site in the apo-structure.
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