The plant pathogen enzyme AldC is a long-chain aliphatic aldehyde dehydrogenase

Abstract

Aldehyde dehydrogenases are versatile enzymes that serve a range of biochemical functions. Although traditionally considered metabolic housekeeping enzymes because of their ability to detoxify reactive aldehydes, like those generated from lipid peroxidation damage, the contributions of these enzymes to other biological processes are widespread. For example, the plant pathogen Pseudomonas syringae strain PtoDC3000 uses an indole-3-acetaldehyde dehydrogenase to synthesize the phytohormone indole-3-acetic acid to elude host responses. Here we investigate the biochemical function of AldC from PtoDC3000. Analysis of the substrate profile of AldC suggests that this enzyme functions as a long-chain aliphatic aldehyde dehydrogenase. The 2.5 Å resolution x-ray crystal of the AldC C291A mutant in a dead-end complex with octanal and NAD+ reveals an apolar binding site primed for aliphatic aldehyde substrate recognition. Functional characterization of site-directed mutants targeting the substrate and NAD(H) binding sites identify key residues in the active site for ligand interactions, including those in the 'aromatic box' that define the aldehyde binding site. Overall, this study provides molecular insight for understanding the evolution of the prokaryotic aldehyde dehydrogenase superfamily and their diversity of function.

Recent Development on Plant Aldehyde Dehydrogenase Enzymes and Their Functions in Plant Development and Stress Signaling

“…Likewise, Pseudomonas syringae strain PtoDC3000 employs an indole-3-acetaldehyde dehydrogenase ( AldA ) to produce auxin indole-3-acetic acid to escape the host defense [ 141 ]. The AldC gene, homologous to AldA, was shown to function as a long-chain aliphatic aldehyde dehydrogenase, which likely contributed to the feeding of the pathogen on the aliphatic compounds in the plant apoplast [ 142 , 143 , 144 ]. Comparative and evolutionary studies of ALDH between plant and fungal or bacterial plant pathogens may help identify lineage-specific inhibitors to target the plant pathogen enzyme and control plant disease.…”

Investigating the reaction and substrate preference of indole-3-acetaldehyde dehydrogenase from the plant pathogen Pseudomonas syringae PtoDC3000

“…Recent work identified the AldC enzyme from P. syringae strain Pto DC3000 as a long-chain aliphatic ALDH [ 28 ]. To compare the activity of AldA with AldC, wild-type AldA was assayed using octanal as a substrate; this is the preferred substrate of AldC [ 28 ]. Although AldA displayed activity with octanal ( Table 2 and Supplementary Figure S2A,B), it was 37-fold less efficient as a substrate compared with indole-3-acetaldehyde.…”

“…This would account for the change in selectivity for octanal as a substrate versus indole-3-acetaldehyde in the AldA F169W mutant. Interestingly, the corresponding residue at this position in AldC from P. syringae , which prefers octanal versus other aliphatic aldehydes as a substrate, is a tryptophan [ 28 ]. Comparison of the k cat / K m for the AldA F169W mutant (2610 M −1 s −1 ) with that of AldC (924 M −1 s −1 ; [ 28 ]) suggest that the identity of the residue at this position of the substrate binding site of these enzymes is critical for substrate preference.…”

“…Biochemical and structural studies of AldC from Pto DC3000 indicate that this enzyme functions as a long-chain aliphatic ALDH and does not contribute to pathogenicity [ 18 , 28 ]. Structural studies of AldA and AldC from Pto DC3000 indicate that both proteins are members of the larger ALDH enzyme superfamily and share a common chemical reaction mechanism, as well as conserved catalytic residues and NAD(H) binding sites with other such enzymes, including human ALDH, but with differences in the substrate binding site ( Figure 1 ) [ 18 , 28 ].…”

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

“…The role of AldA was established to be a nicotinamide adenine dinucleotide (NAD + )-dependent IAAld dehydrogenase that produces IAA [ 11 ]. In 2020, biochemical and structural characterization of AldC by Lee et al revealed it to be a long-chain aliphatic ALDH [ 32 ]. IAA produced by P. syringae has been reported to promote the virulence in Arabidopsis thaliana by two different mechanisms—one, it up-regulates the virulence gene expression in the bacterium, and second, it suppresses salicylic acid-mediated plant defenses by activating auxin signaling in the host plant (via the TIR1/AFB auxin co-receptor system) [ 8 , 11 ].…”