A Novel NADH-dependent and FAD-containing Hydroxylase Is Crucial for Nicotine Degradation by Pseudomonas putida

Hongzhi Tang,Yuxiang Yao,Dake Zhang,Xiangzhou Meng,Lijuan Wang,Hao Yu,Lanying Ma,Ping Xu

doi:10.1074/jbc.m111.283929

Abstract

Nicotine, the main alkaloid produced by Nicotiana tabacum and other Solanaceae, is very toxic and may be a leading toxicant causing preventable disease and death, with the rise in global tobacco consumption. Several different microbial pathways of nicotine metabolism have been reported: Arthrobacter uses the pyridine pathway, and Pseudomonas, like mammals, uses the pyrrolidine pathway. We identified and characterized a novel 6-hydroxy-3-succinoyl-pyridine (HSP) hydroxylase (HspB) using enzyme purification, peptide sequencing, and sequencing of the Pseudomonas putida S16 genome. The HSP hydroxylase has no known orthologs and converts HSP to 2,5-dihydroxy-pyridine and succinic semialdehyde, using NADH. (18)O(2) labeling experiments provided direct evidence for the incorporation of oxygen from O(2) into 2,5-dihydroxy-pyridine. The hspB gene deletion showed that this enzyme is essential for nicotine degradation, and site-directed mutagenesis identified an FAD-binding domain. This study demonstrates the importance of the newly discovered enzyme HspB, which is crucial for nicotine degradation by the Pseudomonas strain.

Highlights

The biochemical mechanism of nicotine biodegradation is important
This study demonstrates the importance of the newly discovered enzyme HspB, which is crucial for nicotine degradation by the Pseudomonas strain
The work described here provides a sound basis for future studies aimed at a better understanding of the molecular principles of nicotine degradation

Summary

Background

The biochemical mechanism of nicotine biodegradation is important. Results: An NADH-dependent and FAD-containing hydroxylase (HspB) for nicotine degradation was purified and mechanistically characterized. Conclusion: The hydroxylase is crucial for nicotine degradation by Pseudomonas putida. We identified and characterized a novel 6-hydroxy-3-succinoyl-pyridine (HSP) hydroxylase (HspB) using enzyme purification, peptide sequencing, and sequencing of the Pseudomonas putida S16 genome. This study demonstrates the importance of the newly discovered enzyme HspB, which is crucial for nicotine degradation by the Pseudomonas strain. The 3-succinoylpyridine is hydroxylated to yield 6-hydroxy-3-succinoylpyridine (HSP), which is converted to 2,5-dihydroxy-pyridine (DHP) and succinate [6, 7] (Fig. 1B). The enzyme HspA activity was relatively low (0.75 ␮M minϪ1 DHP production mgϪ1 protein) [12, 13]. It made us search for another, more active HSP hydroxylase

A Novel Hydroxylase

EXPERIMENTAL PROCEDURES

RESULTS AND DISCUSSION