The Legionella phosphocholinase AnkX modulates IMPDH2 regulation and cytoophidia dynamics

Abstract Legionella pneumophila , the causative agent of Legionnaires’ disease, secretes more than 300 different effector proteins into the host cell to modulate processes such as signal transduction, membrane dynamics, and metabolism. A key regulator of cellular metabolism and proliferation is inosine 5’-monophosphate dehydrogenase type II (IMPDH2), which catalyzes the rate-limiting step of de novo GTP biosynthesis. IMPDH2 assembles into filaments and larger structures known as cytoophidia, which enable fine-tuned regulation of enzymatic activity in response to changing nucleotide demands. Here, we identify human IMPDH2 as a previously unrecognized host target of the Legionella effector AnkX. We show that AnkX post-translationally modifies IMPDH2 within its regulatory domain by covalently attaching a phosphocholine moiety. While this post-translational modification does not alter the catalytic activity of IMPDH2, it disrupts filament formation, thereby impairing nucleotide-dependent regulation of enzyme activity. Consequently, AnkX-mediated phosphocholination affects IMPDH2 filament assembly, cytoophidia formation, and subcellular localization to the specific Legionella -containing vacuole (LCV). Thus, L. pneumophila subverts host GTP metabolism by posttranslationally modifying a central enzyme of the GTP biosynthetic pathway. Graphical abstract description The Legionella effector AnkX post-translationally modifies the human host enzyme IMPDH2 by transferring a phosphocholine group using CDP-choline as co-substrate. We identified the modification site and discovered that this post-translational modification disrupts the ability of IMPDH2 to assemble into filaments and cytoophidia. By shifting the equilibrium toward free octamers, AnkX-mediated PCylation perturbs the structural regulation of IMPDH2 and alters GTP metabolism in L. pneumophila -infected host cells. This figure was inspired by ( https://www.biorxiv.org/content/10.1101/2024.07.29.605679v2 ).