Ligand-triggered allosteric ADP release primes a plant NLR complex

TLDR

We have content for each. Let's aggregate: Background: two lines: "Pathogen recognition by nucleotide-binding (NB), leucine-rich repeat (LRR) receptors (NLRs) plays roles in plant immunity." and "campestris effector AvrAC uridylylates the Arabidopsis PBL2 kinase, and the latter (PBL2UMP) acts as a ligand to activate the NLR ZAR1 precomplexed with the RKS1 pseudokinase." Combine into one sentence: "Pathogen recognition by nucleotide‑binding leucine‑rich repeat receptors (NLRs) is central to plant immunity, and the Xanthomonas campestris effector AvrAC uridylylates Arabidopsis PBL2 kinase, whose uridylylated form (PBL2UMP) serves as a ligand to activate the ZAR1–RKS1 precomplex." That covers both. Purpose: from [Purpose, Mechanism] line: "Here we report the cryo-electron microscopy structures of ZAR1-RKS1 and ZAR1-RKS1-PBL2UMP in an inactive and intermediate state, respectively." So purpose: "The study reports cryo‑EM structures of the ZAR1–RKS1 complex in inactive and intermediate states to elucidate ligand‑triggered activation." That is fine. Mechanism: combine [Mechanism] line: "Recognition of PBL2UMP is exclusively through RKS1, which interacts with ZAR1LRR PBL2UMP binding stabilizes the RKS1 activation segment, which sterically blocks ZAR1 adenosine diphosphate (ADP) binding." Also [Purpose, Mechanism] line includes method. But mechanism: "PBL2UMP is recognized solely by RKS1, whose binding to ZAR1LRR stabilizes its activation segment and sterically blocks ADP binding, thereby priming the complex." Also mention cryo-EM?

Abstract

Pathogen recognition by nucleotide-binding (NB), leucine-rich repeat (LRR) receptors (NLRs) plays roles in plant immunity. The Xanthomonas campestris pv. campestris effector AvrAC uridylylates the Arabidopsis PBL2 kinase, and the latter (PBL2UMP) acts as a ligand to activate the NLR ZAR1 precomplexed with the RKS1 pseudokinase. Here we report the cryo-electron microscopy structures of ZAR1-RKS1 and ZAR1-RKS1-PBL2UMP in an inactive and intermediate state, respectively. The ZAR1LRR domain, compared with animal NLRLRR domains, is differently positioned to sequester ZAR1 in an inactive state. Recognition of PBL2UMP is exclusively through RKS1, which interacts with ZAR1LRR PBL2UMP binding stabilizes the RKS1 activation segment, which sterically blocks ZAR1 adenosine diphosphate (ADP) binding. This engenders a more flexible NB domain without conformational changes in the other ZAR1 domains. Our study provides a structural template for understanding plant NLRs.