Molecular mechanisms of PI4K regulation and their involvement in viral replication

Phosphatidylinositol 4-phosphate; A minor lipid with multiple personalities

Phosphorylated products of phosphatidylinositol (PI), named Diphosphoinositide (DPI) and triphosphoinositide (TPI) were identified long time ago and found to exhibit high turnover rates based on their rapid 32P-phosphate labeling. The PI kinase activities that were responsible for their production were subsequently identified and found to be associated with different organelle membranes, including the plasma membrane. These activities were then linked with a certain group of cell surface receptors that activated phospholipase C enzymes to hydrolyze PI and used calcium or cGMP as a second messenger. This visionary concept was introduced in the seminal BBA review written by Robert Michell, exactly 50 years ago. The enzymology and functional diversity of PI 4-phosphate (PI4P) (the term that has replaced DPI) has since underwent an expansion that could not have been foreseen. In this review I will attempt to revisit this expansion with some historical reflections celebrating the 50th anniversary of the Michell review.

The ACBD3 protein coordinates ER-Golgi contacts to enable productive TBEV infection

Flavivirus infection involves extensive remodeling of the endoplasmic reticulum (ER), which is key to both the replication of the viral RNA genome as well as the assembly and release of new virions. However, little is known about how viral proteins and host factors cooperatively facilitate such a vast transformation of the ER, and how this influences the different steps of the viral life cycle. In this study, we screened for host proteins that were enriched in close proximity to the tick-borne encephalitis virus (TBEV) protein NS4B and found that the top candidates were coupled to trafficking between ER exit sites (ERES) and the Golgi. We characterized the role of ACBD3, one of the identified proteins, and showed that it promotes TBEV infection. Depletion of ACBD3 inhibited virus replication and resulted in abnormal transformation of the ER, leading to reduced virion release. ACBD3's proviral mechanism did not involve the recruitment of PI4PK as previously described for enteroviruses. Instead, productive TBEV infection required the full-length ACBD3, which localizes to ER-Golgi contact sites together with NS4B. We propose that NS4B and ACBD3 promote replication by coordinating the transformation of the ER, which is required for RNA replication and particle release. The transformation involves direct coupling to the Golgi which facilitates efficient virion transport.

IMPORTANCE

Flaviviruses like tick-borne encephalitis have significant effects on human health. During flavivirus infection, the viral particles enter the host cells and transform the endoplasmic reticulum (ER), which is a membranous organelle and the main site of cellular protein synthesis. Although this is critical for successful infection, the details of the process are unknown. Here, we found that the viral protein NS4B and the host protein ACBD facilitate this transformation by ensuring that the ER is coupled to the Golgi apparatus, the organelle responsible for transporting material out of the cell. TBEV uses ACBD3 to guarantee that the connection sites between the transformed ER and the Golgi remain functional so that RNA is replicated and the produced viral particles are exported from the cell and can infect further cells. Our work sheds light both on the basic biology of flavivirus infection, and virus-induced remodeling of membranous organelles.

Unveiling the crossroads of STING signaling pathway and metabolic reprogramming: the multifaceted role of the STING in the TME and new prospects in cancer therapies

The cGAS-STING signaling pathway serves as a critical link between DNA sensing and innate immunity, and has tremendous potential to improve anti-tumor immunity by generating type I interferons. However, STING agonists have shown decreasing biotherapeutic efficacy in clinical trials. Tumor metabolism, characterized by aberrant nutrient utilization and energy production, is a fundamental hallmark of tumorigenesis. And modulating metabolic pathways in tumor cells has been discovered as a therapeutic strategy for tumors. As research concerning STING progressed, emerging evidence highlights its role in metabolic reprogramming, independent its immune function, indicating metabolic targets as a strategy for STING activation in cancers. In this review, we delve into the interplay between STING and multiple metabolic pathways. We also synthesize current knowledge on the antitumor functions of STING, and the metabolic targets within the tumor microenvironment (TME) that could be exploited for STING activation. This review highlights the necessity for future research to dissect the complex metabolic interactions with STING in various cancer types, emphasizing the potential for personalized therapeutic strategies based on metabolic profiling.

Lipid-targeting antiviral strategies: Current state and future perspectives

There is an urgent need for antiviral compounds effective against currently known and future viral threats. The development of host-targeting antivirals (HTAs) appears as an alternative strategy to fight viral infections minimizing the potential of resistant mutant development and potentially leading to the identification of broad-spectrum antiviral agents. Among the host factors explored for HTA strategy, lipids constitute an attractive target as many viruses, even genetically diverse, hijack specific lipids during their lifecycle. Multiple repurposing efforts have been performed to analyze the antiviral properties of lipid-targeting compounds. These studies include the analysis of the effects of cholesterol lowering drugs such as statins, cholesterol transport inhibitors, sphingolipid modulators, de novo lipogenesis inhibitors blocking fatty acid synthesis, compounds targeting glycerophospholipids or drugs interfering with lipid droplet metabolism. This review is focused on the current status of lipid-based or lipid-targeting antiviral strategies and their potential for the development of antiviral therapies, with special emphasis on those studies that have reached advanced stages of development such as efficacy studies in animal models or clinical trials. Whereas there is still a long way to go, multiple proof-of-concept studies and clinical evidence reinforce the therapeutic potential of these strategies warranting their further development into effective antiviral therapies.

Apolipoprotein-L Functions in Membrane Remodeling

The mammalian Apolipoprotein-L families (APOLs) contain several isoforms of membrane-interacting proteins, some of which are involved in the control of membrane dynamics (traffic, fission and fusion). Specifically, human APOL1 and APOL3 appear to control membrane remodeling linked to pathogen infection. Through its association with Non-Muscular Myosin-2A (NM2A), APOL1 controls Golgi-derived trafficking of vesicles carrying the lipid scramblase Autophagy-9A (ATG9A). These vesicles deliver APOL3 together with phosphatidylinositol-4-kinase-B (PI4KB) and activated Stimulator of Interferon Genes (STING) to mitochondrion-endoplasmic reticulum (ER) contact sites (MERCSs) for the induction and completion of mitophagy and apoptosis. Through direct interactions with PI4KB and PI4KB activity controllers (Neuronal Calcium Sensor-1, or NCS1, Calneuron-1, or CALN1, and ADP-Ribosylation Factor-1, or ARF1), APOL3 controls PI(4)P synthesis. PI(4)P is required for different processes linked to infection-induced inflammation: (i) STING activation at the Golgi and subsequent lysosomal degradation for inflammation termination; (ii) mitochondrion fission at MERCSs for induction of mitophagy and apoptosis; and (iii) phagolysosome formation for antigen processing. In addition, APOL3 governs mitophagosome fusion with endolysosomes for mitophagy completion, and the APOL3-like murine APOL7C is involved in phagosome permeabilization linked to antigen cross-presentation in dendritic cells. Similarly, APOL3 can induce the fusion of intracellular bacterial membranes, and a role in membrane fusion can also be proposed for endothelial APOLd1 and adipocyte mAPOL6, which promote angiogenesis and adipogenesis, respectively, under inflammatory conditions. Thus, different APOL isoforms play distinct roles in membrane remodeling associated with inflammation.

Visualizing the dual interaction of calcineurin with PI4KA and FAM126A

In this issue of Structure, Shaw et al.1 visualize the PI4KA-TTC7B-FAM126A-calcineurin complex by combining cryo-EM, HDX-MS, and AlphaFold3, and reveal a dual interaction of calcineurin with PI4KA and FAM126A. This work promotes our understanding of calcineurin-regulated PI4KA activity and paves the way for further exploration of the roles of PI4KA in the plasma membrane.

Bithiazole inhibitors of PI4KB show broad-spectrum antiviral activity against different viral families

Broad-spectrum antivirals can be extremely important for pandemic preparedness. Targeting host factors dispensable for the host but indispensable for the virus can result in high barrier to resistance and a large range of viruses targeted. PI4KB is a lipid kinase involved in the replication of several RNA viruses, but common inhibitors of this target are mainly active against members of the Picornaviridae family. Herein we describe the optimization of bithiazole PI4KB inhibitors as broad-spectrum antivirals (BSAs) active against different members of the Picornaviridae, Coronaviridae, Flaviviridae and Poxviridae families. Since some of these viruses are transmitted via respiratory route, the efficacy of one of the most promising compounds was evaluated in an airway model. The molecule showed complete viral inhibition and absence of toxicity. These results pave the road for the development of new BSAs.

Metabolic channeling of lipids via the contact zones between different organelles

Various lipid transfer proteins (LTPs) mediate the inter-organelle transport of lipids. By working at membrane contact zones between donor and acceptor organelles, LTPs achieve rapid and accurate inter-organelle transfer of lipids. This article will describe the emerging paradigm that the action of LTPs at organelle contact zones generates metabolic channeling events in lipid metabolism, mainly referring to how ceramide synthesized in the endoplasmic reticulum is preferentially metabolized to sphingomyelin in the distal Golgi region, how cholesterol and phospholipids receive specific metabolic reactions in mitochondria, and how the hijacking of host LTPs by intracellular pathogens may generate new channeling-like events. In addition, the article will discuss how the function of LTPs is regulated, exemplified by a few representative LTP systems, and will briefly touch on experiments that will be necessary to establish the paradigm that LTP-mediated inter-organelle transport of lipids is one of the mechanisms of compartmentalization-based metabolic channeling events.

Protein kinase-D1 and downstream signaling mechanisms involved in GLUT4 translocation in cardiac muscle

The Ser/Thr kinase protein kinase-D1 (PKD1) is involved in induction of various cell physiological processes in the heart such as myocellular hypertrophy and inflammation, which may turn maladaptive during long-term stimulation. Of special interest is a key role of PKD1 in the regulation of cardiac substrate metabolism. Glucose and fatty acids are the most important substrates for cardiac energy provision, and the ratio at which they are utilized determines the health status of the heart. Cardiac glucose uptake is mainly regulated by translocation of the glucose transporter GLUT4 from intracellular stores (endosomes) to the sarcolemma, and fatty acid uptake via a parallel translocation of fatty acid transporter CD36 from endosomes to the sarcolemma. PKD1 is involved in the regulation of GLUT4 translocation, but not CD36 translocation, giving it the ability to modulate glucose uptake without affecting fatty acid uptake, thereby altering the cardiac substrate balance. PKD1 would therefore serve as an attractive target to combat cardiac metabolic diseases with a tilted substrate balance, such as diabetic cardiomyopathy. However, PKD1 activation also elicits cardiac hypertrophy and inflammation. Therefore, identification of the events upstream and downstream of PKD1 may provide superior therapeutic targets to alter the cardiac substrate balance. Recent studies have identified the lipid kinase phosphatidylinositol 4-kinase IIIβ (PI4KIIIβ) as signaling hub downstream of PKD1 to selectively stimulate GLUT4-mediated myocardial glucose uptake without inducing hypertrophy. Taken together, the PKD1 signaling pathway serves a pivotal role in cardiac glucose metabolism and is a promising target to selectively modulate glucose uptake in cardiac disease.

The activation of the adaptor protein STING depends on its interactions with the phospholipid PI4P

Activation of the endoplasmic reticulum (ER)-resident adaptor protein STING, a component of a cytosolic DNA-sensing pathway, induces the transcription of genes encoding type I interferons (IFNs) and other proinflammatory factors. Because STING is activated at the Golgi apparatus, control of the localization and activation of STING is important in stimulating antiviral and antitumor immune responses. Through a genome-wide CRISPR interference screen, we found that STING activation required the Golgi-resident protein ACBD3, which promotes the generation of phosphatidylinositol 4-phosphate (PI4P) at the trans-Golgi network, as well as other PI4P-associated proteins. Appropriate localization and activation of STING at the Golgi apparatus required ACBD3 and the PI4P-generating kinase PI4KB. In contrast, STING activation was enhanced when the lipid-shuttling protein OSBP, which removes PI4P from the Golgi apparatus, was inhibited by the US Food and Drug Administration-approved antifungal itraconazole. The increase in the abundance of STING-activating phospholipids at the trans-Golgi network resulted in the increased production of IFN-β and other cytokines in THP-1 cells. Furthermore, a mutant STING that could not bind to PI4P failed to traffic from the ER to the Golgi apparatus in response to a STING agonist, whereas forced relocalization of STING to PI4P-enriched areas elicited STING activation in the absence of stimulation with a STING agonist. Thus, PI4P is critical for STING activation, and manipulating PI4P abundance may therapeutically modulate STING-dependent immune responses.

Identification of inositol monophosphatase as a broad-spectrum antiviral target of ivermectin

Ivermectin has broad-spectrum antiviral activities. Despite the failure in clinical application of COVID-19, it can serve as a lead compound for the development of more effective broad-spectrum antivirals, for which a better understanding of its antiviral mechanisms is essential. We thus searched for potential novel targets of ivermectin in host cells by label-free thermal proteomic profiling using Huh-7 cells. Inositol monophosphatase (IMPase) was found among the proteins with shifted thermal stability by ivermectin. Ivermectin could inhibit IMPase activity and reduce cellular myo-inositol and phosphatidylinositol-4-phosphate levels. On the other hand, inositol could impair the antiviral activity of ivermectin and lithium, an IMPase inhibitor with known antiviral activity. As phosphatidylinositol phosphate is crucial for the replication of many RNA viruses, inhibition of cellular myo-inositol biosynthesis may be an important antiviral mechanism of ivermectin. Hence, inhibition of IMPase could serve as a potential target for broad-spectrum antiviral development.

Highly potent and selective phosphatidylinositol 4-kinase IIIβ inhibitors as broad-spectrum anti-rhinoviral agents

Human rhinoviruses (hRVs) cause upper and lower respiratory tract infections and exacerbate asthma and chronic obstructive pulmonary disease. hRVs comprise more than 160 strains with considerable genetic variation. Their high diversity and strain-specific interactions with antisera hinder the development of anti-hRV therapeutic agents. Phosphatidylinositol-4-kinase IIIβ (PI4KIIIβ) is a key enzyme in the phosphoinositide signalling pathway that is crucial for the replication and survival of various viruses. We identified novel PI4KIIIβ inhibitors, N-(4-methyl-5-arylthiazol)-2-amide derivatives, by generating a hit compound, 1a, from the high-throughput screening of a chemical library, followed by the optimization study of 1a. Inhibitor 7e exhibited the highest activity (EC50 = 0.008, 0.0068, and 0.0076 μM for hRV-B14, hRV-A16, and hRV-A21, respectively) and high toxicity (CC50 = 6.1 μM). Inhibitor 7f showed good activity and low toxicity and provided the highest selectivity index (SI ≥ 4638, >3116, and >2793 for hRV-B14, hRV-A16, and hRV-A21, respectively). Furthermore, 7f showed broad-spectrum activities against various hRVs, coxsackieviruses, and other enteroviruses, such as EV-A71 and EV-D68. The binding mode of the inhibitors was investigated using 7f, and the experimental results of plaque reduction, replicon and cytotoxicity, and time-of-drug-addition assays suggested that 7f acts as a PI4KIIIβ inhibitor. The kinase inhibition activity of this series of compounds against PI4KIIIα and PI4KIIIβ was assessed, and 7f demonstrated kinase inhibition activity with an IC50 value of 0.016 μM for PI4KIIIβ, but not for PI4KIIIα (>10 μM). Therefore, 7f represents a highly potent and selective PI4KIIIβ inhibitor for the further development of antiviral therapy against hRVs or other enteroviruses.

Research progress on phosphatidylinositol 4-kinase inhibitors

Phosphatidylinositol 4-kinases (PI4Ks) could phosphorylate phosphatidylinositol (PI) to produce phosphatidylinositol 4-phosphate (PI4P) and maintain its metabolic balance and location. PI4P, the most abundant monophosphate inositol in eukaryotic cells, is a precursor of higher phosphoinositols and an essential substrate for the PLC/PKC and PI3K/Akt signaling pathways. PI4Ks regulate vesicle transport, signal transduction, cytokinesis, and cell unity, and are involved in various physiological and pathological processes, including infection and growth of parasites such as Plasmodium and Cryptosporidium, replication and survival of RNA viruses, and the development of tumors and nervous system diseases. The development of novel drugs targeting PI4Ks and PI4P has been the focus of the research and clinical application of drugs, especially in recent years. In particular, PI4K inhibitors have made great progress in the treatment of malaria and cryptosporidiosis. We describe the biological characteristics of PI4Ks; summarize the physiological functions and effector proteins of PI4P; and analyze the structural basis of selective PI4K inhibitors for the treatment of human diseases in this review. Herein, this review mainly summarizes the developments in the structure and enzyme activity of PI4K inhibitors.

DGARM/C10orf76/ARMH3 for Ceramide Transfer Zone at the Endoplasmic Reticulum-Distal Golgi Contacts

Phosphatidylinositol 4-monophosphate (PtdIns(4)P) is one of the key membrane components which mark the membrane contact sites. In the mammalian Golgi complex, PtdIns(4)P is produced at various subregions via specific mechanisms for each site. Particularly, PtdIns(4)P pools generated at the distal Golgi regions are pivotal for the determination of membrane contacts between the endoplasmic reticulum (ER) and Golgi, at which inter-organelle lipid transport takes place. In this short review, we will focus on C10orf76 (or ARMH3), which we propose to rename as DGARM after a distal Golgi armadillo repeat protein, for its function in generating a PtdIns(4)P pool crucial for ER-to-distal Golgi ceramide transport. We further discuss from the viewpoint of the evolutionary conservation of DGARM.

Apolipoproteins L1 and L3 control mitochondrial membrane dynamics

Apolipoproteins L1 and L3 (APOLs) are associated at the Golgi with the membrane fission factors phosphatidylinositol 4-kinase-IIIB (PI4KB) and non-muscular myosin 2A. Either APOL1 C-terminal truncation (APOL1Δ) or APOL3 deletion (APOL3-KO [knockout]) reduces PI4KB activity and triggers actomyosin reorganization. We report that APOL3, but not APOL1, controls PI4KB activity through interaction with PI4KB and neuronal calcium sensor-1 or calneuron-1. Both APOLs are present in Golgi-derived autophagy-related protein 9A vesicles, which are involved in PI4KB trafficking. Like APOL3-KO, APOL1Δ induces PI4KB dissociation from APOL3, linked to reduction of mitophagy flux and production of mitochondrial reactive oxygen species. APOL1 and APOL3, respectively, can interact with the mitophagy receptor prohibitin-2 and the mitophagosome membrane fusion factor vesicle-associated membrane protein-8 (VAMP8). While APOL1 conditions PI4KB and APOL3 involvement in mitochondrion fission and mitophagy, APOL3-VAMP8 interaction promotes fusion between mitophagosomal and endolysosomal membranes. We propose that APOL3 controls mitochondrial membrane dynamics through interactions with the fission factor PI4KB and the fusion factor VAMP8.

Structural basis for the conserved roles of PI4KA and its regulatory partners and their misregulation in disease

The type III Phosphatidylinositol 4-kinase alpha (PI4KA) is an essential lipid kinase that is a master regulator of phosphoinositide signalling at the plasma membrane (PM). It produces the predominant pool of phosphatidylinositol 4-phosphate (PI4P) at the PM, with this being essential in lipid transport and in regulating the PLC and PI3K signalling pathways. PI4KA is essential and is highly conserved in all eukaryotes. In yeast, the PI4KA ortholog stt4 predominantly exists as a heterodimer with its regulatory partner ypp1. In higher eukaryotes, PI4KA instead primarily forms a heterotrimer with a TTC7 subunit (ortholog of ypp1) and a FAM126 subunit. In all eukaryotes PI4KA is recruited to the plasma membrane by the protein EFR3, which does not directly bind PI4KA, but instead binds to the TTC7/ypp1 regulatory partner. Misregulation in PI4KA or its regulatory partners is involved in myriad human diseases, including loss of function mutations in neurodevelopmental and inflammatory intestinal disorders and gain of function in human cancers. This review describes an in-depth analysis of the structure function of PI4KA and its regulatory partners, with a major focus on comparing and contrasting the differences in regulation of PI4KA throughout evolution.

PI4KA and PIKfyve: Essential phosphoinositide signaling enzymes involved in myriad human diseases

Lipid phosphoinositides are master regulators of multiple cellular functions. Misregulation of the activity of the lipid kinases that generate phosphoinositides is causative of human diseases, including cancer, neurodegeneration, developmental disorders, immunodeficiencies, and inflammatory disease. This review will present a summary of recent discoveries on the roles of two phosphoinositide kinases (PI4KA and PIKfyve), which have emerged as targets for therapeutic intervention. Phosphatidylinositol 4-kinase alpha (PI4KA) generates PI4P at the plasma membrane and PIKfyve generates PI(3,5)P2 at endo-lysosomal membranes. Both of these enzymes exist as multi-protein mega complexes that are under myriad levels of regulation. Human disease can be caused by either loss or gain-of-function of these complexes, so understanding how they are regulated will be essential in the design of therapeutics. We will summarize insight into how these enzymes are regulated by their protein-binding partners, with a major focus on the unanswered questions of how their activity is controlled.

Beyond PI3Ks: targeting phosphoinositide kinases in disease

Lipid phosphoinositides are master regulators of almost all aspects of a cell's life and death and are generated by the tightly regulated activity of phosphoinositide kinases. Although extensive efforts have focused on drugging class I phosphoinositide 3-kinases (PI3Ks), recent years have revealed opportunities for targeting almost all phosphoinositide kinases in human diseases, including cancer, immunodeficiencies, viral infection and neurodegenerative disease. This has led to widespread efforts in the clinical development of potent and selective inhibitors of phosphoinositide kinases. This Review summarizes our current understanding of the molecular basis for the involvement of phosphoinositide kinases in disease and assesses the preclinical and clinical development of phosphoinositide kinase inhibitors.

Anionic Pulmonary Surfactant Lipid Treatment Inhibits Rhinovirus A Infection of the Human Airway Epithelium

Rhinoviruses (RVs) are major instigators of acute exacerbations of asthma, COPD, and other respiratory diseases. RVs are categorized into three species (RV-A, RV-B, and RV-C), which comprise more than 160 serotypes, making it difficult to develop an effective vaccine. Currently, no effective treatment for RV infection is available. Pulmonary surfactant is an extracellular complex of lipids and proteins that plays a central role in regulating innate immunity in the lung. The minor pulmonary surfactant lipids, palmitoyl-oleoyl-phosphatidylglycerol (POPG) and phosphatidylinositol (PI), are potent regulators of inflammatory processes and exert antiviral activity against respiratory syncytial virus (RSV) and influenza A viruses (IAV). In the current study, we examined the potencies of POPG and PI against rhinovirus A16 (RV-A16) in primary human airway epithelial cells (AECs) differentiated at an air-liquid interface (ALI). After AECs were infected with RV-A16, PI reduced the viral RNA copy number by 70% and downregulated (55-75%) the expression of antiviral (MDA5, IRF7, and IFN-lambda) and CXCL11 chemokine genes. In contrast, POPG only slightly decreased MDA5 (24%) and IRF7 (11%) gene expression but did not inhibit IFN-lambda gene expression or RV-A16 replication in AECs. However, both POPG and PI inhibited (50-80%) IL6 gene expression and protein secretion and CXCL11 protein secretion. PI treatment dramatically attenuated global gene expression changes induced by RV-A16 infection alone in AECs. The observed inhibitory effects were indirect and resulted mainly from the inhibition of virus replication. Cell-type enrichment analysis of viral-regulated genes opposed by PI treatment revealed the PI-inhibited viral induction of goblet cell metaplasia and the virus-induced downregulation of ciliated, club, and ionocyte cell types. Notably, the PI treatment also altered the ability of RV-A16 to regulate the expression of some phosphatidylinositol 4-kinase (PI4K); acyl-CoA-binding, domain-containing (ACBD); and low-density lipoprotein receptor (LDLR) genes that play critical roles in the formation and functioning of replication organelles (ROs) required for RV replication in host cells. These data suggest PI can be used as a potent, non-toxic, antiviral agent for RV infection prophylaxis and treatment.

Investigating how intrinsically disordered regions contribute to protein function using HDX-MS

A large amount of the human proteome is composed of highly dynamic regions that do not adopt a single static conformation. These regions are defined as intrinsically disordered, and they are found in a third of all eukaryotic proteins. They play instrumental roles in many aspects of protein signaling, but can be challenging to characterize by biophysical methods. Intriguingly, many of these regions can adopt stable secondary structure upon interaction with a variety of binding partners, including proteins, lipids, and ligands. This review will discuss the application of Hydrogen-deuterium exchange mass spectrometry (HDX-MS) as a powerful biophysical tool that is particularly well suited for structural and functional characterization of intrinsically disordered regions in proteins. A focus will be on the theory of hydrogen exchange, and its practical application to identify disordered regions, as well as characterize how they participate in protein–protein and protein–membrane interfaces. A particular emphasis will be on how HDX-MS data can be presented specifically tailored for analysis of intrinsically disordered regions, as well as the technical aspects that are critical to consider when designing HDX-MS experiments for proteins containing intrinsically disordered regions.

ARFs get the BioID treatment: what have we been missing?

Li et al present the results of a proximity-interaction screen in mammalian cells for the effector proteins of 25 members of the Arf family of small GTPases. This study has generated an important resource for those working in several areas of cell biology and provided an initial characterisation of two new cellular roles for some of the least well studied members of this family, the regulation of PLD1 by ARL11/14 in phagocytosis, and the regulation of PI4KB by ARL5A/5B in the Golgi.