Cloning, expression and biochemical characterization of a novel amidase from Thauera sinica K11

A novel amidase (TAM) was identified and cloned from the genome of Thauera sinica K11. The recombinant protein was purified to homogeneity by one-step affinity chromatography for up to 26.4-fold with a yield of 38.1%. Gel filtration chromatography and SDS-PAGE revealed that the enzyme was a tetramer with a subunit of approximately 37.5 kDa. The amidase exhibited the maximum acyl transfer activity at 45 °C and pH 7.0, and it was highly stable over a wide pH range of 6.0-11.0. Inhibition of enzyme activity was observed in the presence of metal ions, thiol reagents and organic solvents. TAM showed a broad substrate spectrum toward aliphatic, aromatic and heterocyclic amides. For linear aliphatic monoamides, the acyl transfer activity of TAM was decreased with the extension of the carbon chain length, and thus the highest activity of 228.2 U/mg was obtained when formamide was used as substrate. This distinct selectivity of amidase to linear aliphatic monoamides expanded the findings of signature amidases to substrate specificity.