research papers
Plant acid invertases catalyse the breakdown of sucrose. Their activity is tightly regulated through interaction with specific protein inhibitors. The complex between the cell-wall invertase inhibitor Nt-CIF and its target enzyme is stable only at acidic pH, as found in the plant cell wall. Since the pH in this compartment can be modulated between pH 4 and 6 in planta, the rapid dissociation of the inhibitor-enzyme complex at neutral pH may represent a regulatory event. Here, it is analyzed whether the inhibitory component undergoes structural rearrangements upon changes in the pH environment. Six crystal forms grown at pH 4.6-9.5 and diffracting up to 1.63 Å indicate only small structural changes in CIF. This suggests that complex dissociation at neutral pH is mediated either by rearrangements in the enzyme or by a complex pattern of surface charges in the inhibitor-enzyme binding interface.
Supporting information
PDB references: Nt-CIF, pH 4.6, 2cj4, r2cj4sf; pH 5.0, 2cj5, r2cj5sf; pH 7.0, 1rj1, r1rj1sf; pH 7.0, CdCl2, 1rj4, r1rj4sf; pH 7.5, 2cj6, r2cj6sf; pH 9.0, 2cj7, r2cj7sf; pH 9.5, 2cj8, r2cj8sf