Nitrile hydratase from Pseudomonas putida NRRL-18668 has been purified and characterized. The purified enzyme catalyzes the hydration of 2(S)-(4'-chlorophenyl)-3-methylbutyronitrile at least fifty times faster than that of 2(R)-(4'-chlorophenyl)-3-methylbutyronitrile. This enzyme is a member of the class of nitrile hydratase that contains cobalt. Visible absorption and CD spectra suggest the cobalt exists as a non-corrin low-spin Co3+ ion in a tetragonally-distorted octahedral ligand field. Chemical reduction of the native enzyme results in a species with the EPR signature of a low-spin Co2+ complex. Like the other cobalt-containing nitrile hydratases, this enzyme is relatively stable, maintaining its activity below 35 degrees C, and it shows a broad activity optimum between pH 7.2 and 7.8. The structural genes for this enzyme have been cloned and sequenced. The deduced amino acid sequences for the alpha and beta subunits show 48-63% and 35-41% homology, respectively, to other sequenced nitrile hydratases. In particular, the cysteine residues in the alpha subunit that have been suggested to coordinate the metal ion in the iron-containing nitrile hydratases [Brennan, B. A., Cummings, J. G., Chase, D. B., Turner, I. M., Jr., & Nelson, M. J. (1996) Biochemistry 35, 10068-10077] are conserved in this enzyme, suggesting that this nitrile hydratase, like the enzyme from Rhodococcus rhodochrous J1, is a member of a newly described class of metalloenzymes with Co3+-thiolate ligation [Brennan, B. A., Alms, G., Nelson, M. J., Durney, L. T., & Scarrow, R. C. (1996) J. Am. Chem. Soc. 118, 9194-9195].

Active sites may be regarded as layers of residues, whereby the residues that interact directly with substrate also interact with residues in a second shell, and these in turn interact with residues in a third shell. These residues in the second and third layers may have distinct roles in maintaining the essential chemical properties of the first-shell catalytic residues, particularly their spatial arrangement relative to the substrate binding pocket, and their electrostatic and dynamic properties. The extent to which these remote residues participate in catalysis and precisely how they affect first-shell residues remains unexplored. In order to better understand the roles of second- and third-shell residues in catalysis, we used THEMATICS to identify residues in the second- and third-shells of the Co-type nitrile hydratase from Pseudomonas putida (ppNHase) that may be important for catalysis. Five of these predicted residues, plus three additional, conserved residues that were not predicted, have been conservatively mutated, and their effects studied both kinetically and structurally. All of these eight residues have no direct contact with the active site metal ion or bound substrate. These results demonstrate that three of the predicted second-shell residues, α-Asp164, β-Glu56, and β-His147, and one predicted third-shell residue β-His71, have significant effects on the catalytic efficiency of the enzyme. One of the predicted residues, α-Glu168, and the three residues not predicted, α-Arg170, α-Tyr171, and β-Tyr215, do not show any significant effects on the catalytic efficiency of the enzyme.

We have constructed a vector designed to facilitate the study of protein secretion in Bacillus subtilis. This vector is based on a translational fusion between the expression elements and signal sequence of Bacillus amyloliquefaciens alkaline protease and the mature coding sequence for Escherichia coli alkaline phosphatase (phoA). We show that export of alkaline phosphatase from B. subtilis depends on a functional signal sequence and that alkaline phosphatase activity depends upon secretion. The vector design facilitates the insertion of heterologous coding sequences between the signal and phoA to generate three-part translational fusions. Such phoA fusions are easily analyzed by monitoring alkaline phosphatase activity on agar plates or in culture supernatants or by immunological detection. Exploitation of this methodology, which has proven to be extremely useful in the study of protein secretion in E. coli, has a variety of applications for studying protein secretion in B. subtilis.Fusion proteins which possess an easily assayed activity have proven to be valuable tools for the study of protein secretion in Escherichia coli. For example, translational fusions to lacZ, the E. coli gene coding for P3-galactosidase, have been used extensively in the identification of genes involved in protein secretion and the analysis of signal sequence structure and function (2, 4-6, 29). Hoffman and Wright adapted the utility of fusion proteins for the analysis of protein secretion in E. coli by developing a reporter system based on translational fusions to phoA, the E. coli gene coding for alkaline phosphatase (AP) (13). AP proved to be particularly suited as a reporter in E. coli secretion studies because (i) AP has activity only when secreted, (ii) AP retains activity even with an amino-terminal extension, and (iii) AP is easily detected and assayed even at very low levels. Manoil and Beckwith extended the use of AP as a secretion reporter in E. coli by using a transposon derivative of Tn5 which contains phoA without the promoter and signal sequence (22). The use of phoA fusions has proven to be a powerful tool for the study of protein secretion compatibility, intrinsic membrane topology, protein export signals, and the identification of genes for cell envelope and extracellularly secreted proteins (for a review, see reference 23).Most studies of protein secretion in bacteria have focused on E. coli, but the gram-positive Bacillus species merit investigation since they secrete certain proteins into growth media at high levels (1,26,32). Although this secretion capability has long been important for commercial enzyme production, little is known about the mechanism of protein export in Bacillus species. One reason that protein secretion in Bacillus species has remained largely unexplored is the lack of convenient genetic tools. In this article we present an extension of the phoA fusion technology to the study of protein secretion in Bacillus subtilis. We describe how the various assays for secretion that are based on phoA fus...

A chemoenzymatic process for the production of high-purity glycolic acid has been demonstrated, starting with the reaction of formaldehyde and hydrogen cyanide to produce glycolonitrile in > 99 % yield and purity. The resulting aqueous glycolonitrile was used without further purification in a subsequent biocatalytic conversion of glycolonitrile to ammonium glycolate. A high-activity biocatalyst based on an Acidovorax facilis 72W nitrilase was developed, where protein engineering and optimized protein expression in an E. coli transformant host were used to improve microbial nitrilase specific activity by 33-fold compared to the wild-type strain. A biocatalyst productivity of > 1000 g glycolic acid/g dry cell weight was achieved using a glutaraldehyde/ polyethylenimine cross-linked carrageenan-immobilized E. coli MG1655 transformant expressing the A. facilis 72W nitrilase mutant, where 3.2 M ammonium glycolate was produced in consecutive batch reactions with biocatalyst recycle, or in a continuous stirred-tank reactor. Direct conversion of the unpurified ammonium glycolate product solution to highpurity aqueous glycolic acid was accomplished by fixed-bed ion exchange over a strong acid cation resin.