Cloning, purification, crystallization and preliminary X-ray diffraction analysis of nitrile hydratase from the themophilic Bacillus smithii SC-J05-1.

Nitrile hydratase (NHase) converts nitriles to the corresponding amides and is recognized as having important industrial applications. Purification, cloning, crystallization and initial crystallographic studies of the NHase from Bacillus smithii SC-J05-1 (Bs NHase) were conducted to analyze the activity, specificity and thermal stability of this hydrolytic enzyme. Bs NHase was purified to homogeneity from microbial cells of B. smithii SC-J05-1 and the nucleotide sequences of both the alpha- and beta-subunits were determined. Purified Bs NHase was used for crystallization and several crystal forms were obtained by the vapour-diffusion method. Microseeding and the addition of magnesium ions were essential components to obtain crystals suitable for X-ray diffraction analysis.

Synthesis of Novel Heteroquaterphenoquinones and Their Electrochemical, Structural, and Spectroscopic Characterization.

Novel heteroquaterphenoquinones, 5,5'-bis(3,5-di-tert-butyl-4-oxo-2,5-cyclohexadien-1-ylidene)-5,5'-dihydro-2,2'-bithienyl (3) and its 2,2'-biselenienyl (4), 2,2'-bifuryl (5), and 2,2'-bi-N-methylpyrrolyl (6) analogues, were synthesized by a stepwise cross-coupling reaction or by a more convenient one-pot oxidative homocoupling reaction of heterocycle-substituted phenols. Despite a highly conjugation-extended system, the quinones 3-6 are very stable in the solid state and in solution in common organic solvents. These quinones undergo a reversible one-stage, two-electron reduction up to dianions and a two-stage, one-electron oxidation reaction up to dications. The E(1)(red) of these quinones increases with the increase in the aromaticity of the incorporated heterocycles. The E(1)(ox) of these quinones appears to be specified by the ionization potential of the incorporated heterocycles. Thus, the N-methylquinone 6 exhibiting the lowest E(1)(ox) value exhibits the smallest E(1)(sum) among the quinones 3-6. The quinone 5 was revealed to exist in an unusual O-cis conformation in the solid state by X-ray crystallography, whereas the quinone 3 exists in an S-trans conformation in the solid state. The cis and trans isomers are interconvertible in solution in 3-5, whereas only N-trans isomer was detected for 6 in (1)H NMR spectroscopy. The quinones 3-6 exhibit a very intense absorption maximum in the near-infrared region of 662-827 nm. Of these, the maximum absorption wave length of 6 shifts to a more bathochromic region by 149-165 nm than those of 3-5. The quinones 3-6 can be used as dyestuffs in various fields for laser-driven high-density optical storage media.

The First Heterotriquinone and Dicyanoheterotriquinone Methide That Undergo a Five-Stage Amphoteric Redox Reaction.

The dicyanomethylene group and not the quinone oxygen atoms is the site of the first one-electron reduction for the dicyanohetereotriquinone methide 1, although the dicyanomethylene group is substituted at a cyclopentadienyl-like five-membered ring! Compound 1 is amphoteric and undergoes a five-stage sequence of one-electron redox reactions.

Crystal structure of nitrile hydratase from a thermophilic Bacillus smithii.

The crystal structure of the nitrile hydratase (NHase) from Bacillus smithii SC-J05-1 was determined. Our analysis of the structure shows that some residues that seem to be responsible for substrate recognition are different from those of other NHases. In particular, the Phe52 in the beta subunit of NHase from B. smithii covers the metal center partially like a small lid and narrows the active site cleft. It is well known that the NHase from B. smithii especially prefers aliphatic nitriles for its substrate rather than aromatic ones, and we can now infer that the Phe52 residue may play a key role in the substrate specificity for this enzyme. This finding leads us to suggest that substitution of these residues may alter the substrate specificity of the enzyme.