John Walter Scott

Calmodulin is a highly conserved, calcium (Ca ²⁺ ) sensor protein that is ubiquitous among eukaryotes. Ca ²⁺ binding to Calmodulin induces a conformational change that facilitates interaction with, and activation of, serine/threonine protein kinases, including members of the CaMK family. Recently, Ca ²⁺ ‐Calmodulin binding to one such protein kinase, Checkpoint kinase 2 (CHK2), which is responsible for the regulation of cell cycle progression following DNA damage in mammalian cells, was shown to suppress CHK2 catalytic activity. Here, by applying biochemical, structural mass spectrometry and yeast genetic methods, we identify an analogous mode of inhibition of the fission yeast Schizosaccharomyces pombe CHK2 functional orthologue, Cds1, through direct binding of Ca ²⁺ ‐Calmodulin to the Cds1 kinase domain. Our studies assert an ancestral function for Calmodulin in suppressing the catalytic activity of CHK2 orthologs and highlight a mechanism by which Ca ²⁺ flux can attenuate Cds1 catalytic activity to facilitate exit from the replication checkpoint and promote cell cycle progression.

Salt-Inducible Kinase 3 (SIK3) has emerged as a key regulator of peripheral metabolism, however its cellular and molecular function in regulating body weight and energy metabolism, particularly in hypothalamic neurons, remains unclear and largely unexplored. Here, we demonstrate that SIK3 expression is elevated in the hypothalamus of obese mice. Inactivation of SIK3 specifically in orexigenic NPY neurons reduces food intake, increases energy expenditure, and enhances white adipose tissue browning, resulting in resistance to high-fat diet-induced obesity in mice. Pharmacological inhibition of SIK3 with the inhibitor GLPG3970 in diet-induced obese mice led to significant reductions in body weight and adiposity, primarily due to decreased energy intake, with notable improvements in metabolic health. These effects are linked to enhanced central leptin and insulin signaling, and the dephosphorylation and nuclear translocation of key transcriptional metabolic regulators, CRTC1 and HDAC5. These findings reveal a previously unidentified SIK3-mediated pathway that promotes positive energy balance and suggests SIK3 inhibition may offer therapeutic potential for treating obesity and metabolic disorders.

Autism spectrum disorder (ASD; autism) is a prevalent and heterogeneous neurodevelopmental disorder characterised by social communication difficulties, repetitive behaviour, and restricted interests. For individuals with autism, in particular those who require substantial care-giver support, irritability, heightened sensitivity and aggressive behaviours in response to sensory, social, or environmental triggers can limit access to health, education and community services and impact quality of life. Although gastrointestinal (GI) symptom severity is associated with irritable behaviours in autism, there are few approved medications to address challenging behaviour or comorbid psychiatric disorders, or gut dysfunction in autism. Here, we review the mode of action of drugs undergoing clinical trials for treating irritable behaviour and improving social communication as well as potentially gastrointestinal symptoms in individuals with autism. Repurposed medications such as pimavanserin (an atypical antipsychotic) and the antiparasitic suramin are being trialled for treating irritable behaviours and impaired social interaction, respectively, in autism. NTI164 is a medicinal cannabis-derived biopharmaceutical undergoing clinical safety and efficacy trials for improving social communication and similarly, ML-004 is an investigational drug being assessed for treating social communication deficits. Two other repurposed medications previously utilised for schizophrenia; brexpiprazole and lumateperone, as well as AB-2004, a microbial metabolite sequestering agent (with proposed actions on gut function), are undergoing clinical trials to assess impacts on irritability associated with autism. We also outline emerging findings from clinical studies on the use of gut-targeted small molecules and bacteriophage therapy, prebiotics, probiotic supplementation and faecal microbiota transplantation (FMT), and their potential impact on behavioural symptoms in autism.

Calmodulin (CaM) serves an essential role in eukaryotic cells as a Ca2+ sensor. Ca2+ binding leads to conformation changes in CaM that enable engagement of a repertoire of enzymes and the regulation of their catalytic activities. Classically, Ca2+-CaM binds to an inhibitory pseudosubstrate sequence C-terminal to the kinase domain in members of the Ca2+-CaM-dependent protein kinase (CAMK) family and relieves inhibition to promote catalytic activity. Here, we report an unexpected mechanism by which CaM can bind CHK2 kinase to inhibit its kinase activity. Using biochemical, biophysical and structural mass spectrometry, we identify a direct interaction of Ca2+-CaM with the CHK2 kinase domain that suppresses CHK2 catalytic activity in vitro and identify K373 in CHK2 as crucial for cell proliferation in human cells following DNA damage. Our findings add direct suppression of kinase activity to the repertoire of CaM’s functions, complementing the paradigmatic mechanism of promoting kinase activity through autoinhibitory domain sequestration.

Inhibition of adenosine 5′-monophosphate (AMP)–activated protein kinase (AMPK) is under increasing investigation for its therapeutic potential in many diseases. Existing AMPK inhibitors are however limited, with poor selectivity and substantial off-target effects. Here, we provide mechanistic insights and describe the cellular selectivity of the recently identified AMPK inhibitor BAY-3827. A 2.5-Å cocrystal structure of the AMPK kinase domain with BAY-3827 revealed distinct features including a disulfide bridge between the αD helix Cys ¹⁰⁶ and the activation loop residue Cys ¹⁷⁴ . This bridge appears to stabilize the activation loop such that Asn ¹⁶² repositions the Asp-Phe-Gly (DFG) motif Phe ¹⁵⁸ toward the C-terminal lobe, displacing His ¹³⁷ and disrupting the regulatory spine, promoting an inactive kinase state. In hepatocytes, BAY-3827 blocked AMPK activator (MK-8722)–mediated phosphorylation of ACC1 and corresponding inhibition of lipogenesis. Transcriptome analysis revealed that BAY-3827 down-regulated ~30% of MK-8722–stimulated AMPK-dependent genes. We establish the molecular and cellular basis of BAY-3827’s selectivity and utility for delineating AMPK functions while highlighting its limitations.

Inhibition of AMP-activated protein kinase (AMPK) is under increasing investigation for its therapeutic potential in many diseases, including certain cancers. However, existing AMPK- inhibitors available as tool compounds are largely limited to compound C/dorsomorphin and SBI-0206965, both of which suffer from poor selectivity and off-target effects. Here we describe the structure-based molecular insights and cellular actions of a recently identified potent AMPK inhibitor, BAY-3827. Kinase selectivity profiling and sequence analyses of kinases that are highly or weakly inhibited by BAY-3827 uncovered key conserved residues involved in its inhibitory mechanism. A 2.5 Å co-crystal structure of the AMPK kinase domain (KD)-BAY-3827 complex and comparison with known KD-inhibitor structures, revealed an overlapping site in the ATP-binding pocket and an αC helix-out conformation. A distinct feature of the BAY-3827-bound state is the formation of a disulfide bridge between the αD helix Cys ¹⁰⁶ and the activation loop residue Cys ¹⁷⁴ . This bridge appears to stabilize the activation loop such that Asn ¹⁶² repositions the DFG motif Phe ¹⁵⁸ toward the C-terminal kinase lobe, displacing His ¹³⁷ and disrupting the regulatory spine, thereby promoting an inactive state. In hepatocytes, 2.5-5 μM BAY-3827, but not the structurally resembling inactive BAY-974, fully blocked AMPK activator (MK-8722)-mediated phosphorylation of ACC1 and corresponding inhibition of lipogenesis. Unbiased transcriptome analysis in MK- 8722-treated wild-type and AMPK-null hepatocytes revealed that 5 μM BAY-3827 downregulated >30% of MK-8722-stimulated AMPK-dependent genes. Based on its greater selectivity and potency substantiated by comprehensive structural and cellular investigations, BAY-3827 is a powerful tool to delineate AMPK functions. One-sentence summary: We provide the mechanism of action of the potent and selective AMPK inhibitor BAY-3827, which blocks AMPK-dependent cellular functions.

Protein Serine Kinase H1 (PSKH1) was recently identified as a crucial factor in kidney development and is overexpressed in prostate, lung, and kidney cancers. However, little is known about PSKH1 regulatory mechanisms, leading to its classification as a “dark” kinase. Here, we used biochemistry and mass spectrometry to define PSKH1’s consensus substrate motif, protein interactors, and how interactors, including Ca ²⁺ sensor proteins, promote or suppress activity. Intriguingly, despite the absence of a canonical Calmodulin binding motif, Ca ²⁺ -Calmodulin activated PSKH1 while, in contrast, the ER-resident Ca ²⁺ sensor of the Cab45, Reticulocalbin, Erc55, Calumenin (CREC) family, Reticulocalbin-3, suppressed PSKH1 catalytic activity. In addition to antagonistic regulation of the PSKH1 kinase domain by Ca ²⁺ sensing proteins, we identified UNC119B as a protein interactor that activates PSKH1 via direct engagement of the kinase domain. Our findings identify complementary allosteric mechanisms by which regulatory proteins tune PSKH1’s catalytic activity and raise the possibility that different Ca ²⁺ sensors may act more broadly to tune kinase activities by detecting and decoding extremes of intracellular Ca ²⁺ concentrations.

Calcium (Ca2+) ions are ubiquitous and indispensable signaling messengers that regulate virtually every cell function. The unique ability of Ca2+ to regulate so many different processes yet cause stimulus specific changes in cell function requires sensing and decoding of Ca2+ signals. Ca2+-sensing proteins, such as calmodulin, decode Ca2+ signals by binding and modifying the function of a diverse range of effector proteins. These effectors include the Ca2+-calmodulin dependent protein kinase kinase-2 (CaMKK2) enzyme, which is the core component of a signaling cascade that plays a key role in important physiological and pathophysiological processes, including brain function and cancer. In addition to its role as a Ca2+ signal decoder, CaMKK2 also serves as an important junction point that connects Ca2+ signaling with energy metabolism. By activating the metabolic regulator AMP-activated protein kinase (AMPK), CaMKK2 integrates Ca2+ signals with cellular energy status, enabling the synchronization of cellular activities regulated by Ca2+ with energy availability. Here, we review the structure, regulation, and function of CaMKK2 and discuss its potential as a treatment target for neurological disorders, metabolic disease, and cancer.