Effects of synthetic alkamides on Arabidopsis fatty acid amide hydrolase activity and plant development

Ex vivo lipidomics reveal monoacylglycerols as substrates for a fatty acid amide hydrolase in the legume Medicago truncatula

Fatty acid amide hydrolase (FAAH) is a conserved hydrolase in eukaryotes with promiscuous activity toward a range of acylamide substrates. The native substrate repertoire for FAAH has just begun to be explored in plant systems outside the model Arabidopsis thaliana. Here, we used ex vivo lipidomics to identify potential endogenous substrates for Medicago truncatula FAAH1 (MtFAAH1). We incubated recombinant MtFAAH1 with lipid mixtures extracted from M. truncatula and resolved their profiles via gas chromatography-mass spectrometry (GC-MS). Data revealed that besides N-acylethanolamines (NAEs), sn-1 or sn-2 isomers of monoacylglycerols (MAGs) were substrates for MtFAAH1. Combined with in vitro and computational approaches, our data support both amidase and esterase activities for MtFAAH1. MAG-mediated hydrolysis via MtFAAH1 may be linked to biological roles that are yet to be discovered.

Two legume fatty acid amide hydrolase isoforms with distinct preferences for microbial- and plant-derived acylamides

Fatty acid amide hydrolase (FAAH) is a widely conserved amidase in eukaryotes, perhaps best known for inactivating N-acylethanolamine lipid mediators. However, FAAH enzymes hydrolyze a wide range of acylamide substrates. Analysis of FAAHs from multiple angiosperm species revealed two conserved phylogenetic groups that differed in key conserved residues in the substrate binding pocket. While the foundation group of plant FAAHs, designated FAAH1, has been studied at the structural and functional level in Arabidopsis thaliana, nothing is known about FAAH2 members. Here, we combined computational and biochemical approaches to compare the structural and enzymatic properties of two FAAH isoforms in the legume Medicago truncatula designated MtFAAH1 and MtFAAH2a. Differences in structural and physicochemical properties of the substrate binding pockets, predicted from homology modeling, molecular docking, and molecular dynamic simulation experiments, suggested that these two FAAH isoforms would exhibit differences in their amidohydrolase activity profiles. Indeed, kinetic studies of purified, recombinant MtFAAHs indicated a reciprocal preference for acylamide substrates with MtFAAH1 more efficiently utilizing long-chain acylamides, and MtFAAH2a more efficiently hydrolyzing short-chain and aromatic acylamides. This first report of the enzymatic behavior of two phylogenetically distinct plant FAAHs will provide a foundation for further investigations regarding FAAH isoforms in legumes and other plant species.

Specialized metabolism and development: An unexpected friendship

Plants produce a myriad of metabolites. Some of them have been regarded for a long time as secondary or specialized metabolites and are considered to have functions mostly in defense and the adaptation of plants to their environment. However, in the last years, new research has shown that these metabolites can also have roles in the regulation of plant growth and development, some acting as signals, through the interaction with hormonal pathways, and some independently of them. These reports provide a glimpse of the functional possibilities that specialized metabolites present in the modulation of plant development and encourage more research in this direction.

Beyond the Usual Suspects: Physiological Roles of the Arabidopsis Amidase Signature (AS) Superfamily Members in Plant Growth Processes and Stress Responses

The diversification of land plants largely relies on their ability to cope with constant environmental fluctuations, which negatively impact their reproductive fitness and trigger adaptive responses to biotic and abiotic stresses. In this limiting landscape, cumulative research attention has centred on deepening the roles of major phytohormones, mostly auxins, together with brassinosteroids, jasmonates, and abscisic acid, despite the signaling networks orchestrating the crosstalk among them are so far only poorly understood. Accordingly, this review focuses on the Arabidopsis Amidase Signature (AS) superfamily members, with the aim of highlighting the hitherto relatively underappreciated functions of AMIDASE1 (AMI1) and FATTY ACID AMIDE HYDROLASE (FAAH), as comparable coordinators of the growth-defense trade-off, by balancing auxin and ABA homeostasis through the conversion of their likely bioactive substrates, indole-3-acetamide and N-acylethanolamine.

Fatty Acid Amide Hydrolases: An Expanded Capacity for Chemical Communication?

Fatty acid amide hydrolase (FAAH) is an enzyme that belongs to the amidase signature (AS) superfamily and is widely distributed in multicellular eukaryotes. FAAH hydrolyzes lipid signaling molecules - namely, N-acylethanolamines (NAEs) - which terminates their actions. Recently, the crystal structure of Arabidopsis thaliana FAAH was solved and key residues were identified for substrate-specific interactions. Here, focusing on residues surrounding the substrate-binding pocket, a comprehensive analysis of FAAH sequences from angiosperms reveals a distinctly different family of FAAH-like enzymes. We hypothesize that FAAH, in addition to its role in seedling development, also acts in an N-acyl amide communication axis to facilitate plant-microbe interactions and that structural diversity provides for the flexible use of a wide range of small lipophilic signaling molecules.

Changes in Retinal N-Acylethanolamines and their Oxylipin Derivatives During the Development of Visual Impairment in a Mouse Model for Glaucoma

Neurons are especially susceptible to oxidative damage, which is increasingly implicated in neurodegenerative disease. Certain N-acylethanolamines (NAEs) have been shown to protect neurons from oxidative stress. Since glaucoma may be considered a neurodegenerative disorder and the survival of retinal neurons could also be influenced by N-acylethanolamines, our goal was to quantify changes in certain N-acylethanolamine species and their oxylipin derivatives in the retina of a mouse model for glaucoma. We also sought to identify relationships between these and parameters of glaucoma disease development, specifically intraocular pressure, visual acuity, and contrast sensitivity. Five N-acylethanolamine species and three NAE oxylipin derivatives were quantified in retina from young and aged DBA/2Crl mice. N-Acylethanolamines and NAE-oxylipins in retinal extracts were quantified against deuterated standards by isotope dilution gas chromatography-mass spectrometry. Levels (nmol/g dry weight) of N-arachidonoylethanolamine (anandamide; NAE 20:4) were significantly (p = 0.008) decreased in aged (2.875 ± 0.6702) compared to young animals (5.175 ± 0.971). Conversely, the anandamide oxylipin, 15(S)-HETE ethanolamide (15(S)-HETE EA), was significantly (p = 0.042) increased in aged (0.063 ± 0.009) compared to young animals (0.039 ± 0.011). Enzymatic depletion of the anandamide pool by 15-lipoxygenase and consequent accumulation of 15(S)-HETE ethanolamine may contribute to decreased visual function in glaucomatous mice. Since N-acylethanolamines effectively attenuate glaucoma pathogenesis and associated visual impairment, our data provides additional rationale and novel targets for glaucoma therapies.