Predicted ABA binding to the spinach Rubisco active site.

<p>A) The Rubisco structure was previously solved in the presence of its two 3PGA product molecules (tan sticks with red oxygen atoms and orange phosphorus atoms), which may be used to define the protein’s active site (PDB ID: 1AA1). Small molecule docking of (+)-ABA (cyan sticks with red oxygen atoms) into B) the open, non-activated; C) closed, non-activated (PDB ID: 1RCX); and D) open, activated Rubisco active site, demonstrated the potential for competitive inhibition in a variety of enzyme states. In both non-activated enzyme forms, (+)-ABA was docked to the same location as the 3PGA molecule proximal to Mg2+ (PDB ID: 1AA1, residue 3PG 447) and was stabilized by hydrogen bonding to basic and acid residues (gray sticks) in Rubisco loops. In the activated enzyme form, (+)-ABA was docked to the region between the two 3PGA molecules, making ionic interactions with the Mg2+ cofactor (green spheres).