Phosphorylation of Golgin Imh1 by AMPK/Snf1 compromises Golgi compartmentalization by releasing Arl1-Imh1 axis.

Abstract

Golgins, coiled-coil proteins, are crucial for Golgi architecture and intracellular transport. Mammals have four GRIP-domain-containing Golgins, while budding yeast has a single conserved Golgin, Imh1. Imh1 is recruited to the Golgi membrane by the active small GTPase Arl1 via its GRIP domain. Despite extensive phosphorylation of Imh1 under various stress conditions observed in previous screenings, the biological significance and regulatory mechanisms of Imh1 phosphorylation remain unclear. This study reveals that Snf1, a yeast AMPK homologue, regulates the dissociation of the Arl1-Imh1 axis from the Golgi during glucose deprivation by phosphorylating Imh1 at Ser606, Ser802, and Ser804. The phosphomimetic mutant Imh1^{S606D,S802D,S804D} mislocalizes away from the Golgi, while the phospho-deficient mutant Imh1^{S606A,S802A,S804A}, prevents this mislocalization in an Arl1-dependent manner under glucose deprivation, indicating that this change is not due to Arl1 inactivation. We also provide evidence that AMPK/Snf1 associates with Imh1 and directly phosphorylates Imh1, resulting in conformational change. Furthermore, we demonstrate that AMPK/Snf1-regulated Imh1 phosphorylation impairs its ability to support SNARE recycling in ypt6Δ mutants and compromises Golgi homeostasis. Collectively, these findings reveal how AMPK/Snf1-mediated phosphorylation drives the disassembly of the Arl1-Imh1 axis from the Golgi in response to low-energy conditions, highlighting the critical role of Imh1 phosphorylation in regulating Golgi function.