Key Points• IDH1 promotes leukemogenesis in vivo in cooperation with HoxA9.• Pharmacologic inhibition of mutant IDH1 efficiently inhibits AML cells of IDH1-mutated patients but not of normal CD34 1 bone marrow cells.Mutations in the metabolic enzymes isocitrate dehydrogenase 1 (IDH1) and 2 (IDH2) are frequently found in glioma, acute myeloid leukemia (AML), melanoma, thyroid cancer, and chondrosarcoma patients. Mutant IDH produces 2-hydroxyglutarate (2HG), which induces histone-and DNA-hypermethylation through inhibition of epigenetic regulators. We investigated the role of mutant IDH1 using the mouse transplantation assay. Mutant IDH1 alone did not transform hematopoietic cells during 5 months of observation. However, mutant IDH1 greatly accelerated onset of myeloproliferative disease-like myeloid leukemia in mice in cooperation with HoxA9 with a mean latency of 83 days compared with cells expressing HoxA9 and wild-type IDH1 or a control vector (167 and 210 days, respectively, P 5 .001). Mutant IDH1 accelerated cell-cycle transition through repression of cyclindependent kinase inhibitors Cdkn2a and Cdkn2b, and activated mitogen-activated protein kinase signaling. By computational screening, we identified an inhibitor of mutant IDH1, which inhibited mutant IDH1 cells and lowered 2HG levels in vitro, and efficiently blocked colony formation of AML cells from IDH1-mutated patients but not of normal CD341 bone marrow cells. These data demonstrate that mutant IDH1 has oncogenic activity in vivo and suggest that it is a promising therapeutic target in human AML cells. (Blood.

We introduce a selective and cell-permeable calcium sensor for photoacoustics (CaSPA), a versatile imaging technique that allows for fast volumetric mapping of photoabsorbing molecules with deep tissue penetration. To optimize for Ca-dependent photoacoustic signal changes, we synthesized a selective metallochromic sensor with high extinction coefficient, low quantum yield, and high photobleaching resistance. Micromolar concentrations of Ca lead to a robust blueshift of the absorbance of CaSPA, which translated into an accompanying decrease of the peak photoacoustic signal. The acetoxymethyl esterified sensor variant was readily taken up by cells without toxic effects and thus allowed us for the first time to perform live imaging of Ca fluxes in genetically unmodified cells and heart organoids as well as in zebrafish larval brain via combined fluorescence and photoacoustic imaging.

Despite their near sequence identity, actin isoforms cannot completely replace each other in vivo and show marked differences in their tissue-specific and subcellular localization. Little is known about isoform-specific differences in their interactions with myosin motors and other actin-binding proteins. Mammalian cytoplasmic β- and γ-actin interact with nonsarcomeric conventional myosins such as the members of the nonmuscle myosin-2 family and myosin-7A. These interactions support a wide range of cellular processes including cytokinesis, maintenance of cell polarity, cell adhesion, migration, and mechano-electrical transduction. To elucidate differences in the ability of isoactins to bind and stimulate the enzymatic activity of individual myosin isoforms, we characterized the interactions of human skeletal muscle α-actin, cytoplasmic β-actin, and cytoplasmic γ-actin with human myosin-7A and nonmuscle myosins-2A, -2B and -2C1. In the case of nonmuscle myosins-2A and -2B, the interaction with either cytoplasmic actin isoform results in 4-fold greater stimulation of myosin ATPase activity than was observed in the presence of α-skeletal muscle actin. Nonmuscle myosin-2C1 is most potently activated by β-actin and myosin-7A by γ-actin. Our results indicate that β- and γ-actin isoforms contribute to the modulation of nonmuscle myosin-2 and myosin-7A activity and thereby to the spatial and temporal regulation of cytoskeletal dynamics. FRET-based analyses show efficient copolymerization abilities for the actin isoforms in vitro. Experiments with hybrid actin filaments show that the extent of actomyosin coupling efficiency can be regulated by the isoform composition of actin filaments.

Here, we report that the natural compound pentachloropseudilin (PClP) acts as a reversible and allosteric inhibitor of myosin ATPase and motor activity. IC50 values are in the range from 1 to 5 μm for mammalian class-1 myosins and greater than 90 μm for class-2 and class-5 myosins, and no inhibition was observed with class-6 and class-7 myosins. We show that in mammalian cells, PClP selectively inhibits myosin-1c function. To elucidate the structural basis for PClP-induced allosteric coupling and isoform-specific differences in the inhibitory potency of the compound, we used a multifaceted approach combining direct functional, crystallographic, and in silico modeling studies. Our results indicate that allosteric inhibition by PClP is mediated by the combined effects of global changes in protein dynamics and direct communication between the catalytic and allosteric sites via a cascade of small conformational changes along a conserved communication pathway.

Aberrant actomyosin interactions contribute to a wide range of pathophysiological conditions including heart failure, neurodegenerative disorders, and tumor growth. Despite surgical, interventional, and pharmacological advances, the burden and economic impact of these diseases remains immense. The initiation and progression of these disorders is frequently found to be a direct consequence of aberrant motile activity, which makes the in-depth investigation of the molecular mechanisms underlying actomyosin-dependent motility a prerequisite for the development of innovative treatment strategies. The present review describes key structural features of the actomyosin system, the basis of chemo-mechanical and allosteric coupling in the myosin motor domain, and molecular engineering and small molecule-based approaches to alter myosin function.

Previous studies demonstrated importance of C-mannosylation for efficient protein secretion. To study its impact on protein folding and stability, we analyzed both C-mannosylated and non-C-mannosylated thrombospondin type 1 repeats (TSRs) of netrin receptor UNC-5. In absence of C-mannosylation, UNC-5 TSRs could only be obtained at low temperature and a significant proportion displayed incorrect intermolecular disulfide bridging, which was hardly observed when C-mannosylated. Glycosylated TSRs exhibited higher resistance to thermal and reductive denaturation processes, and the presence of C-mannoses promoted the oxidative folding of a reduced and denatured TSR in vitro. Molecular dynamics simulations supported the experimental studies and showed that C-mannoses can be involved in intramolecular hydrogen bonding and limit the flexibility of the TSR tryptophan-arginine ladder. We propose that in the endoplasmic reticulum folding process, C-mannoses orient the underlying tryptophan residues and facilitate the formation of the tryptophan-arginine ladder, thereby influencing the positioning of cysteines and disulfide bridging.

The small molecule EMD 57033 has been shown to stimulate the actomyosin ATPase activity and contractility of myofilaments. Here, we show that EMD 57033 binds to an allosteric pocket in the myosin motor domain. EMD 57033-binding protects myosin against heat stress and thermal denaturation. In the presence of EMD 57033, ATP hydrolysis, coupling between actin and nucleotide binding sites, and actin affinity in the presence of ATP are increased more than 10-fold. Addition of EMD 57033 to heat-inactivated β-cardiac myosin is followed by refolding and reactivation of ATPase and motile activities. In heat-stressed cardiomyocytes expression of the stress-marker atrial natriuretic peptide is suppressed by EMD 57033. Thus, EMD 57033 displays a much wider spectrum of activities than those previously associated with small, drug-like compounds. Allosteric effectors that mediate refolding and enhance enzymatic function have the potential to improve the treatment of heart failure, myopathies, and protein misfolding diseases.DOI: http://dx.doi.org/10.7554/eLife.01603.001

Myosin activity is crucial for many biological functions. Strong links have been established between changes in the activity of specific myosin isoforms and diseases such as cancer, cardiovascular failure, and disorders of sensory organs and the central nervous system. The modulation of specific myosin isoforms therefore holds a strong therapeutic potential. In recent work, we identified members of the marine alkaloid family of pseudilins as potent inhibitors of myosin-dependent processes. Here, we report the crystal structure of the complex between the Dictyostelium myosin 2 motor domain and 2,4-dichloro-6-(3,4,5-tribromo-1H-pyrrole-2-yl)phenol (3). Detailed comparison with previously solved structures of the myosin 2 complex with bound pentabromopseudilin (2a) or pentachloropseudilin (4a) provides insights into the molecular basis of the allosteric communication between the catalytic and the allosteric sites. Moreover, we describe the inhibitory potency for a congeneric series of halogenated pseudilins. Insight into their mode of action is gained by applying a combination of experimental and computational approaches.