PNNL

Abstract

A plant central metabolic sensor kinase, SUCROSE-NON-FERMENTING1-46 RELATED PROTEIN KINASE1 (SnRK1) phosphorylates its target proteins, effecting 47 a shift from anabolism to catabolism. Trehalose 6-phosphate (T6P) is a proxy for 48 cellular sugar status and a potent inhibitor of SnRK1. T6P binds to KIN10, a SnRK1 49 catalytic subunit, weakening its affinity for its activating kinase, GEMINIVIRUS REP-50 INTERACTING KINASE1 (GRIK1). Here, we investigate the molecular basis for T6P 51 inhibition of KIN10. Molecular dynamics simulations and in vitro phosphorylation 52 assays identified and validated the T6P-binding site on KIN10. Molecular modeling 53 revealed that upon binding of KIN10 to GRIK1, KIN10’s activation loop reorients into 54 GRIK1’s active site, permitting its phosphorylation and activation. Under high-sugar 55 conditions, T6P binds to KIN10, blocks the reorientation of its activation loop, and 56 prevents its phosphorylation and activation by GRIK1. Consequently, T6P inhibition 57 of SnRK1 maintains basal SnRK1 activity, minimizing its phosphorylation activity, 58 thereby causing a general shift from catabolism to anabolism.