amidase

Amidase is an enzyme that catalyzes the hydrolysis of amide bonds (R-CO-NH2), producing a carboxylate and ammonia. As a member of the hydrolase class, amidases participate in nitrogen metabolism and the breakdown of amide-containing compounds across a range of organisms, including bacteria, fungi, and plants.

Many characterized amidases belong to the Amidase Signature (AS) family. They share a highly conserved sequence motif, typically GGSSSG, in which a central serine acts as the nucleophile to form an acyl-enzyme intermediate. A lysine and other active-site residues participate in catalysis, and water ultimately hydrolyzes the acyl-enzyme to release the products. The AS fold is common in both cytosolic and periplasmic enzymes.

Substrates of amidases include short-chain aliphatic amides such as acetamide and propanamide, certain aromatic amides, and other amide-containing compounds encountered in metabolism and the environment. In microbes, amidases enable utilization of amides as nitrogen sources and contribute to xenobiotic degradation and the broader cycling of carbon and nitrogen.

Classification and structure: Amidases are cataloged under the enzyme commission number EC 3.5.1.4. Beyond the AS family, other amidases employ different catalytic strategies and substrates. Structural studies reveal a diversity of architectures, but the hallmark AS enzymes exhibit the signature motif in a conserved loop near the active site.

Applications include bioremediation and biocatalysis for amide bond hydrolysis, with ongoing research into substrate scope, mechanism, and engineering of amidase variants for industrial and environmental uses.