Biophysical characterization of higher plant Rubisco activase.

Rubisco activase (Rca) is a chaperone-like protein of the AAA+ family, which uses mechano-chemical energy derived from ATP hydrolysis to release tightly bound inhibitors from the active site of the primary carbon fixing enzyme ribulose 1,5-bisphosphate oxygenase/carboxylase (Rubisco). Mechanistic and structural investigations of Rca have been hampered by its exceptional thermolability, high degree of size polydispersity and propensity towards subunit aggregation. In this work, we have characterized the thermal stability and self-association behavior of recombinant Rca preparations, and have developed ligand screening methods.

Structural changes associated with the acute thermal instability of Rubisco activase.

Inhibition of photosynthesis by heat has been linked to the instability of the ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) chaperone, Rubisco activase. Examination of the recombinant enzyme showed that ADP and ATP protected against inactivation, whereas Mg(2+) promoted inactivation. Heating caused aggregation of Rubisco activase characterized by disruption of secondary structure content and formation of insoluble protein.