Enzymatic Inhibitors of Aspartyl Protease EAP1 and Xylanase SRXL1 from Sporisorium reilianum Isolated from Corn Seeds

TL;DR

Corn starches from two hybrids inhibit enzymes from a fungus causing corn head smut, offering a potential alternative to chemical fungicides.

Contribution

First report of corn starches inhibiting aspartyl protease and xylanase from Sporisorium reilianum.

Findings

Starches from corn hybrids showed 100% inhibition of EAP1 and SRXL1 enzymes.

Purified starches exhibited uncompetitive inhibition, reducing both Km and Vmax values.

Inhibitory activity was lost after treatment with α-amylase.

Abstract

Corn head smut is a disease caused by the fungus Sporisorium reilianum. Chemical treatments and tolerant hybrids are available for control of this disease; however, these can lead to the development of resistant strains, complicating its management. This microorganism produces two extracellular enzymes—aspartyl protease EAP1 and xylanase SRXL1—which may be involved in the host penetration and colonization processes. Plants produce peptides that inhibit enzymes involved in phytopathogenesis, which could serve as tools to control plant pathogens. In this study, enzyme inhibitors were extracted from corn seed flours derived from two hybrids—a white variety (DK-2061) and a purple variety (BOGUI)—with the objective of evaluating their inhibitory effects on the enzymes EAP1 and SRXL1. Interestingly, the identified inhibitors were starches that showed 100% enzymatic inhibition. These compounds were characterized through Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS) analysis. The purified starches exhibited acetylation (1.52 ± 0.07% for DK-2061 and 1.16 ± 0.04% for BOGUI) as a result of the purification process, due to the use of an acetate regulator; however, they maintained their complete inhibitory activity against the studied enzymes. In contrast, the activity of the purified inhibitors was lost after incubation with α-amylase. Each isolated compound showed uncompetitive inhibition on both enzymatic activities, indicated by a decrease in Km and Vmax values, as determined using the Lineweaver-Burk equation. This represents the first report of the inhibitory effects of corn starches on aspartyl protease and xylanase extracted from S. reilianum. Therefore, these compounds could serve as valuable elements in strategies to manage head smut, potentially reducing the reliance on chemical fungicides.

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