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Figure 5.
FIGURE 5. Equilibrium model for the conformational states
of AT. Similar to the revised model proposed by Chuang et al.
(9), our data support a two-state conformational equilibrium for
AT in the absence of heparin. Ribbon diagrams are given to
represent the one activated and two native states. State N is
the monomeric AT structure presented here with its RCL held
close against the body of AT and the P1 side chain sequestered
in the acidic pocked used as an exosite for factor Xa binding.
This state would be nonreactive toward proteases but is in rapid
equilibrium with state N' (based on the structure of
heterodimeric native AT), where there are fewer contacts to
constrain the RCL and the P1 residue is free to interact with
proteases. Activation of AT by the pentasaccharide results
ultimately in the expulsion of the hinge and the liberation of
the entire RCL. Monomer A is based on the structure of AT in
complex with the pentasaccharide and S195A factor Xa (23).
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