Discovery of the 1-naphthylamine biodegradation pathway reveals an enzyme that catalyzes 1-naphthylamine glutamylation

Abstract

1-Naphthylamine (1NA), which is harmful to human and aquatic animals, has been used widely in the manufacturing of dyes, pesticides, and rubber antioxidants. Nevertheless, little is known about its environmental behavior and no bacteria have been reported to use it as the growth substrate. Herein, we describe a pathway for 1NA degradation in isolate Pseudomonas sp. strain JS3066, determine the structure and mechanism of the enzyme NpaA1 that catalyzes the initial reaction, and reveal how the pathway evolved. From genetic and enzymatic analysis, a cluster of 5 genes encoding a dioxygenase system was determined to be responsible for the initial steps in 1NA degradation through glutamylation of 1NA. The γ-glutamylated 1NA was subsequently oxidized to 1,2-dihydroxynaphthalene which was further degraded by the well-established pathway of naphthalene degradation via catechol. Enzymatic analysis showed that NpaA1 catalyzed conversion of various anilines and naphthylamine derivatives. Structural and biochemical studies of NpaA1 revealed that the broad substrate specificity of NpaA1 is due to a large hydrophobic pocket, which is different from type I glutamine synthetase (GSI). The findings enhance understanding of degrading polycyclic aromatic amines, and will also enable the application of bioremediation at naphthylamine contaminated sites.