Biophysical mechanism of T-cell receptor triggering in a reconstituted system

A T-cell-mediated immune response is initiated by the T-cell receptor (TCR) interacting with peptide-bound major histocompatibility complex (pMHC) on an infected cell. The mechanism by which this interaction triggers intracellular phosphorylation of the TCR, which lacks a kinase domain, remains poorly understood. Here, we have introduced the TCR and associated signalling molecules into a non-immune cell and reconstituted ligand-specific signalling when these cells are conjugated with antigen-presenting cells. We show that signalling requires the differential segregation of a phosphatase and kinase in the plasma membrane. An artificial, chemically controlled receptor system generates the same effect as TCR–pMHC, demonstrating that the binding energy of an extracellular protein–protein interaction can drive the spatial segregation of membrane proteins without a transmembrane conformational change. This general mechanism may extend to other receptors that rely on extrinsic kinases, including, as we demonstrate, chimaeric antigen receptors being developed for cancer immunotherapy.     

Structural basis for gene regulation by a thiamine pyrophosphate-sensing riboswitch

Riboswitches are metabolite-sensing RNAs, typically located in the non-coding portions of messenger RNAs, that control the synthesis of metabolite-related proteins. Here we describe a 2.05 angstroms crystal structure of a riboswitch domain from the Escherichia coli thiM mRNA that responds to the coenzyme thiamine pyrophosphate (TPP). TPP is an active form of vitamin B1, an essential participant in many protein-catalysed reactions. Organisms from all three domains of life, including bacteria, plants and fungi, use TPP-sensing riboswitches to control genes responsible for importing or synthesizing thiamine and its phosphorylated derivatives, making this riboswitch class the most widely distributed member of the metabolite-sensing RNA regulatory system. The structure reveals a complex folded RNA in which one subdomain forms an intercalation pocket for the 4-amino-5-hydroxymethyl-2-methylpyrimidine moiety of TPP, whereas another subdomain forms a wider pocket that uses bivalent metal ions and water molecules to make bridging contacts to the pyrophosphate moiety of the ligand. The two pockets are positioned to function as a molecular measuring device that recognizes TPP in an extended conformation. The central thiazole moiety is not recognized by the RNA, which explains why the antimicrobial compound pyrithiamine pyrophosphate targets this riboswitch and downregulates the expression of thiamine metabolic genes. Both the natural ligand and its drug-like analogue stabilize secondary and tertiary structure elements that are harnessed by the riboswitch to modulate the synthesis of the proteins coded by the mRNA. In addition, this structure provides insight into how folded RNAs can form precision binding pockets that rival those formed by protein genetic factors.     

Effect of dinitrophenol and glucose on amine release from isolated rabbit blood platelets

Zusammenfassung Agar-aktiviertes Kaninchenplasma (Anaphylatoxin) setztin vitro Histamin und Serotonin aus normalen Kaninchenblutplättchen frei. Dieser Effekt ist vom Stoffwechsel der Thrombocyten abhängig, da er durch Dinitrophenol gehemmt wird. Bei Anwesenheit von Glukose wird die Hemmung aufgehoben.     

Relationship of specific granules to the natriuretic and diuretic activity of rat atria

Summary The isolation of several fractions from rat atrial homogenates, by the use of differential and sucrose gradient centrifugation, indicates that the diuretic and natriuretic activity is restricted to the fractions rich in specific granules. Our preliminary results suggest that the active substance is a small peptide which is probably different from the natriuretic substance(s) already known.Supported by a group grant given by the Medical Research Council of Canada to the Multidisciplinary Research Group on Hypertension of the Clinical Research Institute of Montreal.Acknowledgments. The authors thank Suzanne Diebold for technical assistance.     

Structure of the Cul1-Rbx1-Skp1-F boxSkp2 SCF ubiquitin ligase complex

SCF complexes are the largest family of E3 ubiquitin-protein ligases and mediate the ubiquitination of diverse regulatory and signalling proteins. Here we present the crystal structure of the Cul1-Rbx1-Skp1-F boxSkp2 SCF complex, which shows that Cul1 is an elongated protein that consists of a long stalk and a globular domain. The globular domain binds the RING finger protein Rbx1 through an intermolecular beta-sheet, forming a two-subunit catalytic core that recruits the ubiquitin-conjugating enzyme. The long stalk, which consists of three repeats of a novel five-helix motif, binds the Skp1-F boxSkp2 protein substrate-recognition complex at its tip. Cul1 serves as a rigid scaffold that organizes the Skp1-F boxSkp2 and Rbx1 subunits, holding them over 100 A apart. The structure suggests that Cul1 may contribute to catalysis through the positioning of the substrate and the ubiquitin-conjugating enzyme, and this model is supported by Cul1 mutations designed to eliminate the rigidity of the scaffold.     

Disappearance of different substances in contact with the external surface of the brain

Résumé La disparition de différentes substances en contact avec la surface externe du cerveau est étudiée. Les temps moyens de disparition de celles-ci suggèrent l'existence d'une barrière s'opposant au passage de ces substances du compartiment subarachnoïde crânien au tissu nerveux.

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Work supported by grants from the Consejo Nacional de Investigaciones Cientificas y Técnicas (Argentine).     

The use of lytic enzymes ofMicromonospora spp. to prepare protoplasts of yeasts

Résumé On met en évidence pour la première fois l'action lytique d'une espèce deMicromonospora qui a le pouvoir de digérer la paroi cellulaire des levures, donnant lieu à la formation de structures possédant des propriétés de protoplastes. Cette enzyme que nous avons déjà partiellement purifée, montre plus d'activité que d'autres systèmes semblables quant à l'obtention de protoplastes ainsi que de meilleures propriétés.     

Unique physiological and pathogenic features of Leptospira interrogans revealed by whole-genome sequencing

Leptospirosis is a widely spread disease of global concern. Infection causes flu-like episodes with frequent severe renal and hepatic damage, such as haemorrhage and jaundice. In more severe cases, massive pulmonary haemorrhages, including fatal sudden haemoptysis, can occur. Here we report the complete genomic sequence of a representative virulent serovar type strain (Lai) of Leptospira interrogans serogroup Icterohaemorrhagiae consisting of a 4.33-megabase large chromosome and a 359-kilobase small chromosome, with a total of 4,768 predicted genes. In terms of the genetic determinants of physiological characteristics, the facultatively parasitic L. interrogans differs extensively from two other strictly parasitic pathogenic spirochaetes, Treponema pallidum and Borrelia burgdorferi, although similarities exist in the genes that govern their unique morphological features. A comprehensive analysis of the L. interrogans genes for chemotaxis/motility and lipopolysaccharide synthesis provides a basis for in-depth studies of virulence and pathogenesis. The discovery of a series of genes possibly related to adhesion, invasion and the haematological changes that characterize leptospirosis has provided clues about how an environmental organism might evolve into an important human pathogen.