Biology subjects

Loria, P. M.

Publications and source records attributed to Loria, P. M..

3 recordsLinked to original sources

bioRxiv2026

Insight into the scaffolding function of USP18 from a high resolution cryo-EM structure of STAT2-USP18-ISG15 ternary complex

USP18 is a primary negative regulator of the type I interferon (IFN-I) signaling which regulates hundreds of IFN-stimulated genes for viral protection and anti-cancer immunity. USP18 plays dual roles in the IFN-I signaling: 1) deubiquitinase enzymatic function which cleaves ISG15 from its substrates and 2) scaffolding function through forming a complex with STAT2 to suppress IFN-I signaling. Targeting the scaffolding function of USP18, instead of its enzyme activity, is crucial for reducing cancer cell fitness and boosting anti-tumor immunity. However, the molecular basis of USP18s scaffolding function remains unclear due to the lack of structural information. Here, using a fusion tag strategy, we captured the transient USP18-STAT2 complex and determined a ternary complex structure of STAT2-USP18-ISG15 at 3.05 [A] resolution by cryogenic electron microscopy (cryo-EM) that delineated detailed USP18-STAT2 interactions. Remarkably, the ternary complex impairs USP18s enzymatic function by STAT2-mediated disruption of its catalytic triad. Structural analysis and mutagenesis identify specific USP18 point mutations, facilitating further investigation into the role of USP18 in IFN-I signaling. Taken together, our findings suggest that USP18s scaffolding function could present an untapped opportunity for cancer therapy.

molecular biology↗

bioRxiv2021

Molecular basis for the regulation of human glycogen synthase by phosphorylation and glucose-6-phosphate

Glycogen synthase (GYS1), in complex with glycogenin (GYG1), is the central enzyme of muscle glycogen biosynthesis, and its inhibition has been proposed as a therapeutic avenue for various glycogen storage diseases (GSDs). GYS1 activity is inhibited by phosphorylation of its N- and C-termini, which can be relieved by allosteric activation of glucose-6-phosphate. However, the structural basis of GYS1 regulation is unclear. Here, we present the first cryo-EM structures of phosphorylated human GYS1 complexed with a minimal interacting region of GYG1 in the inhibited, activated, and catalytically competent states at resolutions of 3.0-4.0 [A]. These structures reveal how phosphorylations of specific N- and C- terminal residues are sensed by different arginine clusters that lock the GYS1 tetramer complex in an inhibited state via inter-subunit interactions. The allosteric activator, glucose-6-phopshate, promotes a conformational change by disrupting these interactions and increases flexibility of GYS1 allowing for a catalytically competent state to occur when bound to the sugar donor UDP-glucose. We also identify an inhibited-like conformation that has not transitioned into the activated state, whereby the locking interaction of phosphorylation with the arginine cluster impedes the subsequent conformational changes due to glucose-6-phosphate binding. Finally, we show that the PP1 phosphatase regulatory subunit PPP1R3C (PTG) is recruited to the GYS1:GYG1 complex through direct interaction with glycogen. Our results address long-standing questions into the mechanism of human glycogen synthase regulation.

biochemistry↗

bioRxiv2020

A small-molecule oral agonist of the human glucagon-like peptide-1 receptor

Peptide agonists of the glucagon-like peptide-1 receptor (GLP-1R) have revolutionized diabetes therapy, but their use has been limited by the requirement for injection. Here we describe the first effective, orally bioavailable small molecule GLP-1R agonists. A sensitized high-throughput screen identified a series of small molecule GLP-1R agonists that were optimized to promote endogenous GLP-1R signaling with nM potency. These small molecule agonists increased insulin levels in primates but not rodents, which is explained by a cryo-EM structure that revealed a binding pocket requiring primate-specific tryptophan 33. Importantly, oral administration of agonist PF-06882961 to healthy humans produced dose-dependent declines in serum glucose (NCT03309241). This opens the door to a new era of oral small molecule therapies that target the well-validated GLP-1R pathway for metabolic health. One Sentence SummaryPF-06882961 is an orally administered small molecule that activates the GLP-1 receptor to lower blood glucose in humans.

pharmacology and toxicology↗