# Identification and NMR-based structural characterization of the functional domain of EPC3, a virulence effector of the phytopathogenic fungus Colletotrichum orbiculare

## TL;DR

This paper identifies the functional part of a protein from a plant fungus and reveals its structure using NMR, helping understand how it causes disease.

## Contribution

The NMR structure of the functional domain of EPC3 and its dynamic properties are reported for the first time.

## Key findings

- The N-terminal half domain of EPC3 is responsible for its function.
- The EPC3 functional domain has five β-strands and three disulfide bonds.
- Disulfide bonds are crucial for maintaining the structural integrity of EPC3.

## Abstract

Plant pathogens secrete various effector proteins to induce infections in their host plants. Understanding the molecular basis of plant pathogen effectors is important for improving agricultural productivity, plant health, and sustainability. However, this remains a significant challenge. EPC3 (EPC; Effector Protein for Cucurbit infection) is a recently discovered effector involved in the virulence of the cucurbit anthracnose fungus Colletotrichum orbiculare on host plants, although the structure-function relationship is unknown. Here, we report that the N-terminal half domain of EPC3 is responsible for its function. We determined the solution nuclear magnetic resonance (NMR) structure and dynamic properties of this functional domain. The structure containing three disulfide (SS) bonds is composed of five β-strands. The molecule was rigid except for the loop regions connecting β-strands. The structural properties were compared with those of other structurally similar effectors to deduce the potential residues responsible for this function. Furthermore, mutation experiments demonstrated the importance of intramolecular disulfide bonds in maintaining the structural integrity of EPC3. Our results provided insights into the molecular characteristics of EPC3 and a basis for future structure-guided functional studies.