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.
Subject(s)
Amidohydrolases/chemistry , Amidohydrolases/metabolism , Fatty Acids/metabolism , Micrococcaceae/enzymology , Amidohydrolases/genetics , Amino Acid Sequence , Antarctic Regions , Catalytic Domain , Cluster Analysis , Crystallography, X-Ray , DNA, Bacterial/chemistry , DNA, Bacterial/genetics , DNA, Ribosomal/chemistry , DNA, Ribosomal/genetics , Enzyme Stability , Hydrogen-Ion Concentration , Micrococcaceae/growth & development , Micrococcaceae/isolation & purification , Models, Molecular , Molecular Sequence Data , Phylogeny , Protein Multimerization , Protein Structure, Quaternary , RNA, Ribosomal, 16S/genetics , Sequence Alignment , Sequence Analysis, DNA , Sodium Chloride/metabolism , Soil Microbiology , Substrate Specificity , TemperatureABSTRACT
The immunological properties of bovine phospholipase A2 were investigated in order to locate possible sequential epitopes. Polyvalent antiserum raised against the enzyme was tested for its interaction with synthetic peptides derived from regions adopting hydrogen-bonded secondary structures within the tertiary structure of phospholipase A2. The conformations of each peptide in various solvents were determined by CD and ir spectroscopy in order to relate immunological to structural properties. It was found that sequential epitopes are absent in this enzyme, but that region 90-109 could be a possible T-cell epitope through the formation of an amphipathic alpha-helix.
