Molecular characterization of a thermostable aldehyde dehydrogenase (ALDH) from the hyperthermophilic archaeon Sulfolobus tokodaii strain 7.

Aldehyde dehydrogenase (ALDH) is a widely distributed enzyme in nature. Although many ALDHs have been reported until now, the detailed enzymatic properties of ALDH from Archaea remain elusive. Herein, we describe the characterization of an ALDH from the hyperthermophilic archaeon Sulfolobus tokodaii. The enzyme (stALDH) could utilize various aldehydes as substrates, and maximal activity was found with acetaldehyde and the coenzyme NAD. The optimal temperature and pH were 80 °C and 8, respectively, and high thermostability was found with the half-life at 90 °C to be 4 h. The enzyme was considerably resistant to nitroglycerin (GTN) inhibition, which could be restored by reducing agent DTT or (±)-α-lipoic acid. Coenzyme NAD or NADP could regulate the enzymatic thermostability, as well as the esterase activity. Molecular modeling suggested that the enzyme harbored similar structural arrangement with its eukaryotic and bacterial counterparts. Sequence alignment showed the conserved catalytic residues E240 and C274 and cofactor interactive sites N142, K165, I168 and E370, the function of which were verified by site-directed mutagenesis analysis. This is the most thermostable ALDH reported until now and the unique property of this enzyme is potentially beneficial in the fields of biotechnology and biomedicine.