Double agent indole-3-acetic acid: mechanistic analysis of indole-3-acetaldehyde dehydrogenase AldA that synthesizes IAA, an auxin that aids bacterial virulence

Abstract

The large diversity of organisms inhabiting various environmental niches on our planet are engaged in a lively exchange of biomolecules, including nutrients, hormones, and vitamins. In a quest to survive, organisms that we define as pathogens employ innovative methods to extract valuable resources from their host leading to an infection. One such instance is where plant-associated bacterial pathogens synthesize and deploy hormones or their molecular mimics to manipulate the physiology of the host plant. This commentary describes one such specific example - the mechanism of the enzyme AldA, an aldehyde dehydrogenase (ALDH) from the bacterial plant pathogen Pseudomonas syringae which produces the plant auxin hormone indole-3-acetic acid (IAA) by oxidizing the substrate indole-3-acetaldehyde (IAAld) using the cofactor NAD+ (Bioscience Reports, 2020, 40, https://doi.org/10.1042/BSR20202959). Using mutagenesis, enzyme kinetics, and structural analysis, Zhang K. et al., establish that the progress of the reaction hinges on the formation of two distinct conformations of NAD(H) during the reaction course. Additionally, a key mutation in the AldA active site ‘aromatic box’ changes the enzyme’s preference for an aromatic substrate to an aliphatic one. Our commentary concludes that such molecular level investigations help to establish the nature of the dynamics of NAD(H) in ALDH-catalysed reactions, and further show that key active site residues control substrate specificity. We also contemplate that insights from this study can be used to engineer novel ALDH enzymes for environmental, health and industrial applications.

Pseudomonas flavocrustae sp. nov., an endophyte with plant growth promoting traits isolated from Passiflora incarnata

“…Two genes associated with the synthesis of the enzyme aldehyde dehydrogenase were detected. This enzyme oxides indole-3-acetaldehyde in IAA 24 . Also, a gene (COG0679) encoding an auxin efflux carrier was annotated.…”

Endogenous Hormone Levels and Transcriptomic Analysis Reveal the Mechanisms of Bulbil Initiation in Pinellia ternata

“…In the first step of the tryptamine biosynthesis pathway of IAA, TDC catalyzes tryptophan to tryptamine [ 70 ]. ALDH encodes the enzyme that catalyzes indole-3-acetaldehyde to IAA [ 71 ]. The transduction of the IAA signal depends on three protein families: Aux/IAA, TIR1/AFB, and ARF .…”

Intestinal tryptophan metabolism in disease prevention and swine production

“…IPYA is then sequentially converted into indole-3-lactic acid (ILA), indole acrylic acid (IA), and indole-3-propionic acid (IPA) under the activation of phenyllactate dehydrogenase (FldH), phenyllactate dehydratase (FldBC), and acyl-CoA dehydrogenase (AcdA), respectively ( Covarrubias et al., 2021 ). Moreover, Trp decarboxylase 1 is involved in metabolizing L-Trp to tryptamine, which is further converted to IAAld via the activation of Trp decarboxylase (TDC) ( Shah et al., 2021 ). Additionally, IAA and IPA can conjugate with glutamine or glycine to further produce indolyl-acetyl-glutamine, which is oxidized to IAld by peroxidase-catalyzed aerobic oxidation, and indolyl-acryloyl-glycine (IAcrGly) in the liver or kidney ( Mello et al., 1980 ).…”