Figure 2.

Representations of the SbCAD4 active site. A, Coordination of catalytic Zn²⁺ of the open form subunit. In the absence of NADP⁺, Cys-47, His-69, Glu-70, and Cys-165 form tetrahedral coordination around the catalytic Zn²⁺. B, Coordination of catalytic Zn²⁺ of the closed form subunit. In the presence of NADP⁺, the position of the catalytic Zn²⁺ was shifted toward NADP⁺. Coordination between the zinc ion and the carboxylic oxygen of Glu-70 was replaced with formate. C, NADP⁺ in the SbCAD4 active site. The proton-shuttling system is shown as dotted lines, and the bound NADP⁺ is shown as green sticks. Molecular graphics images were produced using the UCSF Chimera package.