Ikuya Shiromizu

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.

Crystallization and preliminary X-ray crystallographic studies of NADP-dependent 3-hydroxyisobutyrate dehydrogenase from Thermus thermophilus HB8

3-Hydroxyisobutyrate, a central metabolite in the valine catabolic pathway, is reversibly oxidized to methylmalonate semialdehyde by a specific NADP-dependent dehydrogenase (HIBADH). HIBADH from Thermus thermophilus HB8 has been overexpressed in Escherichia coli and crystallized by the microbatch method using lithium chloride as a precipitant at 296 K. X-ray diffraction data have been collected to 1.80 A resolution at 100 K using synchrotron radiation. The crystals belong to the orthorhombic space group P2(1)2(1)2(1), with unit-cell parameters a = 85.878, b = 106.367, c = 168.639 A. A homotetramer of HIBADH is likely to be present in the asymmetric unit, giving a V(M) of 3.0 A(3) Da(-1) and a solvent content of 59.3%.