Abstract
Monomethylamine (MMA) is an important climate-active oceanic trace gas and ubiquitous in the oceans. γ-Glutamylmethylamide synthetase (GmaS) catalyzes the conversion of MMA to γ-glutamylmethylamide, the first step in MMA metabolism in many marine bacteria. The gmaS gene occurs in ∼23% of microbial genomes in the surface ocean and is a validated biomarker to detect MMA-utilizing bacteria. However, the catalytic mechanism of GmaS has not been studied because of the lack of structural information. Here, the GmaS from Rhodovulum sp. 12E13 (RhGmaS) was characterized, and the crystal structures of apo-RhGmaS and RhGmaS with different ligands in five states were solved. Based on structural and biochemical analyses, the catalytic mechanism of RhGmaS was explained. ATP is first bound in RhGmaS, leading to a conformational change of a flexible loop (Lys287-Ile305), which is essential for the subsequent binding of glutamate. During the catalysis of RhGmaS, the residue Arg312 participates in polarizing the γ-phosphate of ATP and in stabilizing the γ-glutamyl phosphate intermediate; Asp177 is responsible for the deprotonation of MMA, assisting the attack of MMA on γ-glutamyl phosphate to produce a tetrahedral intermediate; and Glu186 acts as a catalytic base to abstract a proton from the tetrahedral intermediate to finally generate glutamylmethylamide. Sequence analysis suggested that the catalytic mechanism of RhGmaS proposed in this study has universal significance in bacteria containing GmaS. Our results provide novel insights into MMA metabolism, contributing to a better understanding of MMA catabolism in global carbon and nitrogen cycles.
Highlights
Monomethylamine (MMA) is an important climate-active oceanic trace gas and ubiquitous in the oceans. γ-Glutamylmethylamide synthetase (GmaS) catalyzes the conversion of MMA to γ-glutamylmethylamide, the first step in MMA metabolism in many marine bacteria
During the catalysis of GmaS from Rhodovulum sp. 12E13 (RhGmaS), the residue Arg312 participates in polarizing the γ-phosphate of ATP and in stabilizing the γ-glutamyl phosphate intermediate; Asp177 is responsible for the deprotonation of MMA, assisting the attack of MMA on γ-glutamyl phosphate to produce a tetrahedral intermediate; and Glu186 acts as a catalytic base to abstract a proton from the tetrahedral intermediate to generate glutamylmethylamide
The recombinant RhGmaS was active to catalyze the ligation of MMA and glutamate to produce GMA, with ATP and Mg2+ as cofactors
Summary
Received for publication, September 7, 2020, and in revised form, October 23, 2020 Published, Papers in Press, November 16, 2020, https://doi.org/10.1074/jbc.RA120.015952 Ning Wang1,2, Xiu-Lan Chen1,3, Chao Gao1, Ming Peng1, Peng Wang2,3, Na Zhang4, Fuchuan Li5, Gui-Peng Yang6, Qing-Tao Shen4, Shengying Li1, Yin Chen7, Yu-Zhong Zhang1,2,3 , and Chun-Yang Li2,3,* From the 1State Key Laboratory of Microbial Technology, Marine Biotechnology Research Center, Shandong University, Qingdao, China; 2College of Marine Life Sciences, and Frontiers Science Center for Deep Ocean Multispheres and Earth System, Ocean University of China, Qingdao, China; 3Laboratory for Marine Biology and Biotechnology, Pilot National Laboratory for Marine Science and Technology, Qingdao, China; 4School of Life Science and Technology, iHuman Institute, ShanghaiTech University, Shanghai, China; 5National Glycoengineering Research Center and Shandong Key Laboratory of Carbohydrate Chemistry and Glycobiology, Shandong University, Qingdao, China; 6Frontiers Science Center for Deep Ocean Multispheres and Earth System, Key Laboratory of Marine Chemistry Theory and Technology, Ministry of Education, Ocean University of China, Qingdao, China; and 7School of Life Sciences, University of Warwick, Coventry, United Kingdom
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