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L-Lysine dehydrogenases catalyze the oxidative deamination of L-Lysine in the presence of NAD and so far two types of dehydrogenases were discovered. Thermophile and hyperthermophilic microorganisms were screened for a more stable form of L-Lysine dehydrogenase and results are discussed.

Researchers describe a dye-linked dehydrogenase from a thermophilic bacterium that reduces 2,6-dichloroindophenol in the presence of L-proline. This enzyme could be useful in biosensors and may be more stable than its counterpart in mesophilic bacteria.

A study was conducted to examine glutamate dehydrogenase distribution in hyperthermophilic archaea. A Shimadzu 160A spectrophotometer was utilized to assay enzyme activities while glutamate dehydrogenase was purified by Pyrobaculum islandicum at room temperature. The ability of enzymes to catalyze the oxidative deamination of various alpha-amino acids and the reduction amination of various 2-oxo acids was also investigated.

A study was conducted to examine the effects of silicic acid on the growth of Thermus thermophilus TMY, an extreme thermophile isolated from a siliceous deposit formed from geothermal water at a geothermal power plant in Japan. A silica-induced protein (Sip) isolated from the cell envelope fraction of log-phase TMY cells grown in the presence of supersaturated silicic acid offer new insight into the growth and biosilisification associated with thermophiles in geothermal environments.

Genes encoding from 2-deoxy-D-ribose-5-phosphate aldolases (DERAs) from two hyperthermophiles, the archaeon Pyrobaculum aerophilum and the bacterium Thermotoga maritima, are compared with Escherichia coli DERA in terms of their capacity to catalyze aldol condensation. The two enzymes from hyperthermophiles are highly resistant to acetaldehyde and have displayed greater catalysis of sequential aldol condensation of three acetaldehydes than the Escherichia coli enzyme, even at room temperature.

The gene (PH1074) encoding the NAD kinase of the hyperthermophilic archaeon Pyrococcus horikoshii was identified in the genome database, cloned and functionally expressed in Escherichia coli. The deduced amino acid sequence showed a low level of identity to those of Escherichia coli ATP-dependant NAD kinase and the inorganic polyphosphate/ATP-dependent NAD kinase from a hyperthermophilic archaeon.

l-Tryptophan dehydrogenase from Nostoc punctiforme NIES-2108 (NpTrpDH), despite exhibiting high amino acid sequence identity (>30%)/homology (>50%) with NAD(P) + -dependent l-Glu/l-Leu/l-Phe/l-Val dehydrogenases, exclusively catalyzes reversible oxidative deamination of l-Trp to 3-indolepyruvate in the presence of NAD + Here, we determined the crystal structure of the apo form of NpTrpDH. The structure of the NpTrpDH monomer, which exhibited high similarity to that of l-Glu/l-Leu/l-Phe dehydrogenases, consisted of a substrate-binding domain (domain I, residues 3 to 133 and 328 to 343) and an NAD + /NADH-binding domain (domain II, residues 142 to 327) separated by a deep cleft. The apo-NpTrpDH existed in an open conformation, where domains I and II were apart from each other. The subunits dimerized themselves mainly through interactions between amino acid residues around the β-1 strand of each subunit, as was observed in the case of l-Phe dehydrogenase. The binding site for the substrate l-Trp was predicted by a molecular docking simulation and validated by site-directed mutagenesis. Several hydrophobic residues, which were located in the active site of NpTrpDH and possibly interacted with the side chain of the substrate l-Trp, were arranged similarly to that found in l-Leu/l-Phe dehydrogenases but fairly different from that of an l-Glu dehydrogenase. Our crystal structure revealed that Met-40, Ala-69, Ile-74, Ile-110, Leu-288, Ile-289, and Tyr-292 formed a hydrophobic cluster around the active site. The results of the site-directed mutagenesis experiments suggested that the hydrophobic cluster plays critical roles in protein folding, l-Trp recognition, and catalysis. Our results provide critical information for further characterization and engineering of this enzyme., Importance: In this study, we determined the three-dimensional structure of l-Trp dehydrogenase, analyzed its various site-directed substitution mutants at residues located in the active site, and obtained the following informative results. Several residues in the active site form a hydrophobic cluster, which may be a part of the hydrophobic core essential for protein folding. To our knowledge, there is no previous report demonstrating that a hydrophobic cluster in the active site of any l-amino acid dehydrogenase may have a critical impact on protein folding. Furthermore, our results suggest that this hydrophobic cluster could strictly accommodate l-Trp. These studies show the structural characteristics of l-Trp dehydrogenase and hence would facilitate novel applications of l-Trp dehydrogenase., (Copyright © 2016 American Society for Microbiology.)