Aspartic Protease Functions in Plant Defense Mechanisms

Aspartic proteases are a diverse class of proteolytic enzymes characterised by two aspartate residues at the catalytic centre and a conserved sequence motif. In plants, these enzymes play multifaceted roles in developmental programmes and biotic stress responses. Central to their defensive function is the plant-specific insert (PSI), a saposin-like domain that mediates pH-dependent membrane interactions, promoting vesicle fusion or disruption of pathogen membranes. Upon pathogen recognition, aspartic proteases are upregulated by phytohormones such as salicylic acid and abscisic acid, and directed to the apoplast or vacuolar compartments, where they process defence-related peptides, modulate programmed cell death and generate antimicrobial fragments. Additional layers of regulation include redox-dependent processing and inhibitor binding by pathogen-secreted proteases, underscoring a dynamic interplay between plant and invader. Recent advances have elucidated structural transitions that underpin protease activation, the contribution of disulfide bonds to saposin-like domain stability and the evolutionary diversification of aspartic protease subfamilies, including nepenthesin-type enzymes. The global significance of these enzymes is emphasised by their roles in crop resistance, post-harvest quality and potential biotechnological applications as natural antifungal agents and precision molecular scissors in biomass processing.

Research from Nature Portfolio

Recent studies have provided atomic-resolution insights into the saposin-like domain of a potato aspartic protease. It has been shown that acidification triggers a transition from a monomeric to a dimeric open saposin fold, facilitating bilayer fusion under reducing conditions. Detailed characterisation of individual helical segments revealed that a minimal helix within the domain is sufficient to induce membrane perturbation, affording specificity for anionic lipid interfaces. This work demonstrates that pH-dependent conformational switching underlies the targeting and activation of defence-related proteases, and identifies discrete bilayer-active motifs that may be exploited for synthetic antimicrobial design.

Aspartic Protease Functions in Plant Defense Mechanisms publication trend

The graph below shows the total number of articles in aspartic protease functions in plant defense mechanisms across all publications each year (not limited to Nature Index journals).

Technical terms

Aspartic protease: A class of proteolytic enzymes that utilise two aspartate residues at the active site to catalyse peptide bond hydrolysis, implicated in plant development and defence.

Plant-specific insert (PSI): A saposin-like domain of approximately 100 amino acids found in many plant aspartic proteases, responsible for pH-dependent membrane interactions.

Saposin-like fold: A protein fold comprising four to five α-helices stabilised by disulfide bonds, capable of adopting open or closed conformations for membrane binding.

Nepenthesins: A subgroup of plant aspartic proteases with distinctive sequence motifs, initially discovered in carnivorous plants and noted for their stability and potential antifungal activity.

Apoplast: The extracellular continuum in plant tissues, including cell walls and intercellular spaces, through which defence enzymes and metabolites traverse.

References

1. Defense and Offense Strategies: The Role of Aspartic Proteases in Plant–Pathogen Interactions. Biology (2021).
2. The role of disulfide bonds in a Solanum tuberosum saposin-like protein investigated using molecular dynamics. PLOS ONE (2020).
3. Protein Structure Insights into the Bilayer Interactions of the Saposin-Like Domain of Solanum tuberosum Aspartic Protease. Scientific Reports (2017).
4. Response of an aspartic protease gene OsAP77 to fungal, bacterial and viral infections in rice. Rice (2014).
5. Molecular Properties and New Potentials of Plant Nepenthesins. Plants (2020).
6. The Saposin-like Domain of the Plant Aspartic Proteinase Precursor Is a Potent Inducer of Vesicle Leakage*. Journal of Biological Chemistry (2000).