Use of Molecular Dynamics to Decipher the Binding of Salicylic Acid to Proteins. Example of Arabidopsis Thaliana Chloroplastic GAPDH-A1 ^†

Salicylic acid (SA) has an essential role in the responses of plants to pathogens. SA initiates defense signaling cascades by binding to proteins. NPR1 is a transcriptional coactivator and is a key target of SA binding. Many other proteins have been shown to bind SA. Among these proteins are important enzymes of primary metabolism. Here, we describe that the A1 isomer of chloroplast glyceraldehyde 3-phosphate dehydrogenase (GAPA1) from Arabidopsis thaliana binds SA, as shown in surface plasmon resonance experiments. Additionally, we show that SA inhibits its GAPDH activity in vitro. To gain an insight into the underlying molecular interactions and binding mechanism, we combined in silico molecular docking experiments and molecular dynamics simulations on the free protein and protein–ligand complex. The molecular docking analysis led to the identification of two putative binding pockets for SA. A simulation in water of the complex between SA and the protein allowed us to determine that only one pocket, a surface cavity around Asn35, would efficiently bind SA in the presence of a solvent. The importance of this is further supported through experimental biochemical assays. Indeed, mutating GAPA1 Asn35 into Gly or Arg81 into Leu strongly diminished the ability of the enzyme to bind SA. The very same cavity is responsible for the binding of NADP⁺ to GAPA1. NADH inhibited, in a dose-response manner, the binding of SA to GAPA1, validating our data. The use of the methodology to study SA binding to other proteins will be discussed at the end of the talk.