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Unique aliphatic amidase from a psychrotrophic and haloalkaliphilic nesterenkonia isolate.

ABSTRACT: Nesterenkonia strain AN1 was isolated from a screening program for nitrile- and amide-hydrolyzing microorganisms in Antarctic desert soil samples. Strain AN1 showed significant 16S rRNA sequence identity to known members of the genus. Like known Nesterenkonia species, strain AN1 was obligately alkaliphilic (optimum environmental pH, 9 to 10) and halotolerant (optimum environmental Na(+) content, 0 to 15% [wt/vol]) but was also shown to be an obligate psychrophile with optimum growth at approximately 21°C. The partially sequenced genome of AN1 revealed an open reading frame (ORF) encoding a putative protein member of the nitrilase superfamily, referred to as NitN (264 amino acids). The protein crystallized readily as a dimer and the atomic structure of all but 10 amino acids of the protein was determined, confirming that the enzyme had an active site and a fold characteristic of the nitrilase superfamily. The protein was screened for activity against a variety of nitrile, carbamoyl, and amide substrates and was found to have only amidase activity. It had highest affinity for propionamide but demonstrated a low catalytic rate. NitN had maximal activity at 30°C and between pH 6.5 and 7.5, conditions which are outside the optimum growth range for the organism.

SUBMITTER: Nel AJ

PROVIDER: S-EPMC3127607 | biostudies-literature | 2011 Jun

REPOSITORIES: biostudies-literature

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Unique aliphatic amidase from a psychrotrophic and haloalkaliphilic nesterenkonia isolate.

Nel A J M AJ Tuffin I M IM Sewell B T BT Cowan D A DA

Applied and environmental microbiology 20110415 11

Nesterenkonia strain AN1 was isolated from a screening program for nitrile- and amide-hydrolyzing microorganisms in Antarctic desert soil samples. Strain AN1 showed significant 16S rRNA sequence identity to known members of the genus. Like known Nesterenkonia species, strain AN1 was obligately alkaliphilic (optimum environmental pH, 9 to 10) and halotolerant (optimum environmental Na(+) content, 0 to 15% [wt/vol]) but was also shown to be an obligate psychrophile with optimum growth at approxima ...[more]

PMID: 21498772

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Project description:1. Chloroacetone (I) was shown to be an active-site-directed inhibitor of the aliphatic amidase (EC 3.5.1.4) from Pseudomonas aeruginosa strain PAC142.2. This inhibitor reacted with the enzyme in two stages: the first involving the reversible formation of an enzymically inactive species, EI, and the second the formation of a species, EX, from which enzymic activity could not be recovered. 3. Different types of kinetic experiment were conducted to test conformity of the reaction to the scheme: E + I k+1 Equilibrium k-1 EI Leads to K+2 EX A computer-based analysis of the results was carried out and values of the individual rate constants were determined. 4. No direct evidence for a binding step before the formation of EI could be obtained, as with [E]0 Less Than [I]0 the observed first-order rate constant for the formation of EI was directly proportional to the concentration of chloroacetone up to 1.2 mM (above this concentration the reaction became too rapid to follow even by the stopped-flow method developed to investigate fast inhibition). 5. The value of k+1 exhibited a bell-shaped pH-dependency with a maximum value of about 3 X 10(3) M-1. S-1 at pH6 and apparent pKa values of 7.8 and about 4.8.6. The values of k-1 and K+2 were similar and changed with the time of reaction from values of about 3 X 10(-3) S-1 (pH8.6) at short times to about one-sixth this value for longer periods of incubation. In this respect the simple reaction scheme is insufficient to describe the inhibition process. 7. The overall inhibition reaction is rapid, whether it is considered in relation to the expected chemical reactivity of chloroacetone, the rate of reaction of other enzymes with substrate analogues containing the chloromethyl group, or the rate of the amidase-catalysed hydrolysis of N-methylacetamide, a substrate that is nearly isosteric with chloroacetone. 8. Acetamide protected the amidase from inhibition by chloroacetone, and the concentration-dependence of the protection gave a value of an apparent dissociation constant similar to the Km value for this substrate. 9. Addition of acetamide to solutions of the species EI led to a slow recovery of activity. Recovery of active enzyme was also observed after dilution of a solution of EI in the absence of substrate. 10. The species EI is considered not to be a simple adsorption complex, and the possibilities are discussed that it may be a tetrahedral carbonyl adduct, a Schiff base (azomethine) or a complex in which the enzyme has undergone a structural change. The species EX is probably a derivative in which there is a covalent bond between a group in the enzyme and the C-1 atom of the inhibitor.

Dataset Information

Unique aliphatic amidase from a psychrotrophic and haloalkaliphilic nesterenkonia isolate.

Publications

Unique aliphatic amidase from a psychrotrophic and haloalkaliphilic nesterenkonia isolate.

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