Arabidopsis immunity regulator EDS1 in a PAD4/SAG101-unbound form is a monomer with an inherently inactive conformation

J Struct Biol. 2019 Dec 1;208(3):107390. doi: 10.1016/j.jsb.2019.09.007. Epub 2019 Sep 21.

Abstract

In plant innate immunity, enhanced disease susceptibility 1 (EDS1) integrates all pathogen-induced signals transmitted by TIR-type NLR receptors. Driven by an N-terminal α/β-hydrolase-fold domain with a protruding interaction helix, EDS1 assembles with two homologs, phytoalexin-deficient 4 (PAD4) and senescence-associated gene 101 (SAG101). The resulting heterodimers are critical for EDS1 function and structurally well characterized. Here, we resolve solution and crystal structures of unbound Arabidopsis thaliana EDS1 (AtEDS1) using nanobodies for crystallization. These structures, together with gel filtration and immunoprecipitation data, show that PAD4/SAG101-unbound AtEDS1 is stable as a monomer and does not form the homodimers recorded in public databases. Its PAD4/SAG101 anchoring helix is disordered unless engaged in protein/protein interactions. As in the complex with SAG101, monomeric AtEDS1 has a substrate-inaccessible esterase triad with a blocked oxyanion hole and without space for a covalent acyl intermediate. These new structures suggest that the AtEDS1 monomer represents an inactive or pre-activated ground state.

Keywords: Enhanced disease susceptibility 1 (EDS1); Nanobody; Plant innate immunity; Pseudo-enzyme; Senescence-associated gene 101 (SAG101); α/β-Hydrolase fold.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Arabidopsis Proteins / chemistry*
  • Arabidopsis Proteins / genetics
  • Arabidopsis Proteins / metabolism*
  • Carboxylic Ester Hydrolases / chemistry
  • Carboxylic Ester Hydrolases / metabolism*
  • Chromatography, Gel
  • Crystallization
  • DNA-Binding Proteins / chemistry*
  • DNA-Binding Proteins / genetics
  • DNA-Binding Proteins / metabolism
  • Nicotiana / genetics
  • Plants, Genetically Modified
  • Protein Conformation
  • Scattering, Small Angle
  • Single-Domain Antibodies
  • X-Ray Diffraction

Substances

  • Arabidopsis Proteins
  • DNA-Binding Proteins
  • EDS1 protein, Arabidopsis
  • Single-Domain Antibodies
  • Carboxylic Ester Hydrolases
  • PAD4 protein, Arabidopsis
  • SAG101 protein, Arabidopsis