Structure of aldolase from Thermus thermophilus HB8 showing the contribution of oligomeric state to thermostability

2-Deoxyribose-5-phosphate aldolase catalyzes a reversible aldol condensation of two aldehydes via formation of a covalent Schiff-base intermediate at the active lysine residue. The crystal structure of 2-deoxyribose-5-phosphate aldolase from Thermus thermophilus HB8 has been determined with and without the substrate at atomic resolution. This enzyme, which has a unique homotetramer structure, has been compared with the previously reported crystal structures of two orthologues from Escherichia coli and Aeropyrum pernix. In contrast to the similar alpha/beta-barrel fold of the monomers, substantial quaternary structural differences are observed between these three enzymes. Further comparison of the subunit - subunit interface areas of these aldolases showed a clear positive correlation between the interface area and the living temperature of the source organism. From these results, it is concluded that the oligomeric state of 2-deoxyribose-5- phosphate aldolase is important for the thermostability and not for the catalytic function.