Structure of a hyperthermostable dimeric archaeal Rubisco from Hyperthermus butylicus

The crystal structure of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) from the hyperthermophilic archaeon Hyperthermus butylicus is presented at 1.8 Å resolution. Previous structures of archaeal Rubisco have been found to assemble into decamers, and this oligomerization was thought to be required for a highly thermally stable enzyme. In the current study, H. butylicus Rubisco is shown to exist as a dimer in solution, yet has a thermal denaturation midpoint of 114°C, suggesting that high thermal stability can be achieved without an increased oligomeric state. This increased thermal stability appears to be due to an increased number of electrostatic interactions within the monomeric subunit. As such, H. butylicus Rubisco presents a well characterized system in which to investigate the role of assembly and thermal stability in enzyme function.