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

Soon Goo Lee,Joseph M Jez,Jagdeesh S Kottapalli,Michael Duan,Barbara N Kunkel,Kate Harline,Regina Liu,Abhinav Srinath,Sakirat O Akadri,Cynthia K Holland,Orchid Abar,Chris D Raciti,Alexander G Bastian,Jesse Kao,Sheri A Mcclerkin,Shwetha Sudhakar,Vinay Penna,Seong Ho Pahng,Amanda R Groziak,Caroline M Focht,Hui-Yuan S Chen,Matthew C Leong,Wilhelm S Cruz ,Joy J Lin,Barrie Cascella,Brian R Cox,Albert F Mo,Joseph D Tang,Joanna E Luo,Christine Meyer

doi:10.1074/jbc.ra120.014747

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 identifies 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.

Highlights

In all organisms, the diversification of large superfamilies of enzymes provides a foundation for the evolution of biochemical capacity and the ability to metabolize varied small molecules [1]
The NCBI Conserved Protein Domain Family server places AldC in the cd01738/ALDH_CddD_SSP0762 family, 1 of 42 aldehyde dehydrogenase families found in the Pseudomonas [31, 32]
Because many Pseudomonas species evolved to grow under unfavorable environmental conditions, they evolved metabolic diversity and plasticity to use a variety of nutrient sources, to detoxify toxic organic chemicals, and to produce multiple specialized metabolites, including polymers and small molecule compounds [31, 44]

Summary

Introduction

The diversification of large superfamilies of enzymes provides a foundation for the evolution of biochemical capacity and the ability to metabolize varied small molecules [1]. The aromatic aldehyde substrates hydrocinnamaldehyde and indole-3-acetaldehyde were poorly used by AldC with catalytic efficiencies comparable with valeraldehyde and 4-pyridinecarboxaldehyde used with a kcat/Km value 6-fold lower than octanal (Table 1).

Results

Conclusion