Deletion of nine carboxy-terminal residues of the Rubisco small subunit decreases thermal stability but does not eliminate function

A recent X-ray crystal structure of ribulose-1,5-bisphosphate carboxylase/oxygenase from the green alga Chlamydomonas reinhardtii lacks 13 carboxy-terminal residues of the small subunit. To determine the importance of this divergent region, a non-sense mutation was created that removes nine residues. This engineered gene was transformed into a Chlamydomonas strain that lacks the small-subunit gene family. The resulting holoenzyme has a normal CO2/O-2 specificity but decreased carboxylation V-max. Whereas wild-type enzyme retained most of its carboxylase activity after a 10-min incubation at 55degreesC, the mutant enzyme was inactivated. Thus, although disordered or divergent, the carboxy terminus is required for maximal activity and stability. (C) 2002 Published by Elsevier Science B.V. on behalf of the Federation of European Biochemical Societies.