Dynamics in the Phytophthora capsici Effector AVR3a11 Confirm the Core WY Domain Fold

TL;DR

This paper confirms the structural and dynamic properties of the AVR3a11 effector protein from Phytophthora capsici, showing how its flexibility may aid in evading plant defenses.

Contribution

The study provides a detailed structural and dynamic analysis of AVR3a11, confirming the core WY domain fold and its functional flexibility.

Findings

AVR3a11 forms a four-helix bundle confirmed by X-ray crystallography.

Hydrogen/deuterium exchange experiments show the N-terminal helix is less stable than others.

Conformational exchange in AVR3a11 occurs in slow/intermediate time scales, possibly linked to function.

Abstract

Oomycete pathogens cause large economic losses in agriculture
through
diseases such as late blight (Phytophthora infestans), and stem and root rot of soybean (Phytophthora
sojae). The effector protein AVR3a, from P. infestans, and its homologue AVR3a11 from Phytophthora capsici, are host-translocated effectors
that interact with plant proteins to evade defense mechanisms and
enable infection. Both proteins belong to the family of RXLR effectors
and contain an N-terminal secretion signal, an RXLR motif for translocation
into the host cell, and a C-terminal effector domain. Within this
family, many proteins have been predicted to contain one or more WY
domains as their effector domain, which is proposed to encompass a
conserved minimal core fold containing three helices, further stabilized
by additional helices or dimerization. In AVR3a11, a helical N-terminal
extension to the core fold forms a four-helix bundle, as determined
by X-ray crystallography. For a complete picture of the dynamics of
AVR3a11, we have determined the solution structure of AVR3a11, and
studied its dynamics in the fast time scale (ns–ps, from NMR
relaxation parameters) and in the slow time scale (seconds to minutes,
from hydrogen/deuterium exchange experiments). Hydrogen/deuterium
exchange showed that the N-terminal helix is less stable than the
other three helices, confirming the core fold originally proposed.
Relaxation measurements confirm that AVR3a11 undergoes extensive conformational
exchange, despite the uniform presence of fast motions in the spectral
density function throughout most of its sequence. As functional residues
are in the more mobile regions, flexibility in the slow/intermediate
time scale may be functionally important.

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