Human mutations that truncate the massive sarcomere protein titin [TTN-truncating variants (TTNtvs)] are the most common genetic cause for dilated cardiomyopathy (DCM), a major cause of heart failure and premature death. Here we show that cardiac microtissues engineered from human induced pluripotent stem (iPS) cells are a powerful system for evaluating the pathogenicity of titin gene variants. We found that certain missense mutations, like TTNtvs, diminish contractile performance and are pathogenic. By combining functional analyses with RNA sequencing, we explain why truncations in the A-band domain of TTN cause DCM, whereas truncations in the I band are better tolerated. Finally, we demonstrate that mutant titin protein in iPS cell–derived cardiomyocytes results in sarcomere insufficiency, impaired responses to mechanical and β-adrenergic stress, and attenuated growth factor and cell signaling activation. Our findings indicate that titin mutations cause DCM by disrupting critical linkages between sarcomerogenesis and adaptive remodeling. Authors: John T. Hinson, Anant Chopra, Navid Nafissi, William J. Polacheck, Craig C. Benson, Sandra Swist, Joshua Gorham, Luhan Yang, Sebastian Schafer, Calvin C. Sheng, Alireza Haghighi, Jason Homsy, Norbert Hubner, George Church, Stuart A. Cook, Wolfgang A. Linke, Christopher S. Chen, J. G. Seidman, Christine E. Seidman

A challenge of synthetic biology is the creation of cooperative microbial systems that exhibit population-level behaviors. Such systems use cellular signaling mechanisms to regulate gene expression across multiple cell types. We describe the construction of a synthetic microbial consortium consisting of two distinct cell types—an “activator” strain and a “repressor” strain. These strains produced two orthogonal cell-signaling molecules that regulate gene expression within a synthetic circuit spanning both strains. The two strains generated emergent, population-level oscillations only when cultured together. Certain network topologies of the two-strain circuit were better at maintaining robust oscillations than others. The ability to program population-level dynamics through the genetic engineering of multiple cooperative strains points the way toward engineering complex synthetic tissues and organs with multiple cell types. Authors: Ye Chen, Jae Kyoung Kim, Andrew J. Hirning, Krešimir Josić, Matthew R. Bennett

Changes to the symbiotic microbiota early in life, or the absence of it, can lead to exacerbated type 2 immunity and allergic inflammations. Although it is unclear how the microbiota regulates type 2 immunity, it is a strong inducer of proinflammatory T helper 17 (TH17) cells and regulatory T cells (Tregs) in the intestine. Here, we report that microbiota-induced Tregs express the nuclear hormone receptor RORγt and differentiate along a pathway that also leads to TH17 cells. In the absence of RORγt+ Tregs, TH2-driven defense against helminths is more efficient, whereas TH2-associated pathology is exacerbated. Thus, the microbiota regulates type 2 responses through the induction of type 3 RORγt+ Tregs and TH17 cells and acts as a key factor in balancing immune responses at mucosal surfaces. Authors: Caspar Ohnmacht, Joo-Hong Park, Sascha Cording, James B. Wing, Koji Atarashi, Yuuki Obata, Valérie Gaboriau-Routhiau, Rute Marques, Sophie Dulauroy, Maria Fedoseeva, Meinrad Busslinger, Nadine Cerf-Bensussan, Ivo G. Boneca, David Voehringer, Koji Hase, Kenya Honda, Shimon Sakaguchi, Gérard Eberl

T regulatory cells that express the transcription factor Foxp3 (Foxp3+ Tregs) promote tissue homeostasis in several settings. We now report that symbiotic members of the human gut microbiota induce a distinct Treg population in the mouse colon, which constrains immuno-inflammatory responses. This induction—which we find to map to a broad, but specific, array of individual bacterial species—requires the transcription factor Rorγ, paradoxically, in that Rorγ is thought to antagonize FoxP3 and to promote T helper 17 (TH17) cell differentiation. Rorγ’s transcriptional footprint differs in colonic Tregs and TH17 cells and controls important effector molecules. Rorγ, and the Tregs that express it, contribute substantially to regulating colonic TH1/TH17 inflammation. Thus, the marked context-specificity of Rorγ results in very different outcomes even in closely related cell types. Authors: Esen Sefik, Naama Geva-Zatorsky, Sungwhan Oh, Liza Konnikova, David Zemmour, Abigail Manson McGuire, Dalia Burzyn, Adriana Ortiz-Lopez, Mercedes Lobera, Jianfei Yang, Shomir Ghosh, Ashlee Earl, Scott B. Snapper, Ray Jupp, Dennis Kasper, Diane Mathis, Christophe Benoist

A weekly roundup of information on newly offered instrumentation, apparatus, and laboratory materials of potential interest to researchers.

On this week's show: The origin of moralizing gods, replicating 100 psychology experiments, and a roundup of daily news stories.

Defining the morphological characteristics—such as the size, shape, or structure—of different cell types has played a key role in assessing the progression and status of various diseases. Imaging flow cytometry combines the visual analysis capabilities of microscopy with flow cytometry to provide researchers with a powerful tool to study cell morphology and the potential effects of therapeutic interventions. In this webinar, we will explore ways to characterize cell morphology and how this information can be applied to better understand blood disorders, including how erythrocyte morphology is used in the analysis of sickle cell disease and to identify functional intermediates in erythropoiesis.View the Webinar Authors: Kathleen E. McGrath, David Archer

Author: Joan W. Bennett

Abstract

C. elegans MnSOD-3 has been implicated in the longevity pathway and its mechanism of catalysis is relevant to the aging process and carcinogenesis. The structures of MnSOD-3 provide unique crystallographic evidence of a dynamic region of the tetrameric interface (residues 41–54). We have determined the structure of the MnSOD-3-azide complex to 1.77-Å resolution. Analysis of this complex shows that the substrate analog, azide, binds end-on to the manganese center as a sixth ligand and that it ligates directly to a third and new solvent molecule also positioned within interacting distance to the His30 and Tyr34 residues of the substrate access funnel. This is the first structure of a eukaryotic MnSOD-azide complex that demonstrates the extended, uninterrupted hydrogen-bonded network that forms a proton relay incorporating three outer sphere solvent molecules, the substrate analog, the gateway residues, Gln142, and the solvent ligand. This configuration supports the formation and release of the hydrogen peroxide product in agreement with the 5-6-5 catalytic mechanism for MnSOD. The high product dissociation constant k4 of MnSOD-3 reflects low product inhibition making this enzyme efficient even at high levels of superoxide.

Abstract

The disease oculopharyngeal muscular dystrophy is caused by alanine codon trinucleotide expansions in the N-terminal segment of the nuclear poly(A) binding protein PABPN1. As histochemical features of the disease, intranuclear inclusions of PABPN1 have been reported. Whereas the purified N-terminal domain of PABPN1 forms fibrils in an alanine-dependent way, fibril formation of the full-length protein occurs also in the absence of alanines. Here, we addressed the question whether the stability of the RNP domain or domain swapping within the RNP domain may add to fibril formation. A variant of full-length PABPN1 with a stabilizing disulfide bond at position 185/201 in the RNP domain fibrillized in a redox-sensitive manner suggesting that the integrity of the RNP domain may contribute to fibril formation. Thermodynamic analysis of the isolated wild-type and the disulfide-linked RNP domain showed two state unfolding/refolding characteristics without detectable intermediates. Quantification of the thermodynamic stability of the mutant RNP domain pointed to an inverse correlation between fibril formation of full-length PABPN1 and the stability of the RNP domain.

Abstract

Membrane protein crystallography is notoriously difficult due to challenges in protein expression and issues of degradation and structural stability. We have developed a novel method for large-scale screening of native sources for integral membrane proteins that have intrinsic biochemical properties favorable for crystallization. Highly expressed membrane proteins that are thermally stable and nonaggregating in detergent solutions were identified by mass spectrometry from Escherichia coli, Saccharomyces cerevisiae, and Sus scrofa cerebrum. Many of the membrane proteins identified had been crystallized previously, supporting the promise of the approach. Most identified proteins have known functions and include high-value targets such as transporters and ATPases. To validate the method, we recombinantly expressed and purified the yeast protein, Yop1, which is responsible for endoplasmic reticulum curvature. We demonstrate that Yop1 can be purified with the detergent dodecylmaltoside without aggregating.

by Zachary A. King, Andreas Dräger, Ali Ebrahim, Nikolaus Sonnenschein, Nathan E. Lewis, Bernhard O. Palsson

Escher is a web application for visualizing data on biological pathways. Three key features make Escher a uniquely effective tool for pathway visualization. First, users can rapidly design new pathway maps. Escher provides pathway suggestions based on user data and genome-scale models, so users can draw pathways in a semi-automated way. Second, users can visualize data related to genes or proteins on the associated reactions and pathways, using rules that define which enzymes catalyze each reaction. Thus, users can identify trends in common genomic data types (e.g. RNA-Seq, proteomics, ChIP)—in conjunction with metabolite- and reaction-oriented data types (e.g. metabolomics, fluxomics). Third, Escher harnesses the strengths of web technologies (SVG, D3, developer tools) so that visualizations can be rapidly adapted, extended, shared, and embedded. This paper provides examples of each of these features and explains how the development approach used for Escher can be used to guide the development of future visualization tools.

by Jeffrey R. Johnson, Silvia D. Santos, Tasha Johnson, Ursula Pieper, Marta Strumillo, Omar Wagih, Andrej Sali, Nevan J. Krogan, Pedro Beltrao

The African clawed frog Xenopus laevis is an important model organism for studies in developmental and cell biology, including cell-signaling. However, our knowledge of X. laevis protein post-translational modifications remains scarce. Here, we used a mass spectrometry-based approach to survey the phosphoproteome of this species, compiling a list of 2636 phosphosites. We used structural information and phosphoproteomic data for 13 other species in order to predict functionally important phospho-regulatory events. We found that the degree of conservation of phosphosites across species is predictive of sites with known molecular function. In addition, we predicted kinase-protein interactions for a set of cell-cycle kinases across all species. The degree of conservation of kinase-protein interactions was found to be predictive of functionally relevant regulatory interactions. Finally, using comparative protein structure models, we find that phosphosites within structured domains tend to be located at positions with high conformational flexibility. Our analysis suggests that a small class of phosphosites occurs in positions that have the potential to regulate protein conformation.

Journal of the American Chemical SocietyDOI: 10.1021/jacs.5b06300

Journal of the American Chemical SocietyDOI: 10.1021/jacs.5b07203

Journal of the American Chemical SocietyDOI: 10.1021/jacs.5b06645

Journal of the American Chemical SocietyDOI: 10.1021/jacs.5b06558

Journal of the American Chemical SocietyDOI: 10.1021/jacs.5b06507

Journal of the American Chemical SocietyDOI: 10.1021/jacs.5b07823

Journal of the American Chemical SocietyDOI: 10.1021/jacs.5b06658