Mechanism of force generation by myosin heads in skeletal muscle

Muscles generate force and shortening in a cyclical interaction between the myosin head domains projecting from the myosin filaments and the adjacent actin filaments. Although many features of the dynamic performance of muscle are determined by the rates of attachment and detachment of myosin and actin, the primary event in force generation is thought to be a conformational change or 'working stroke' in the actin-bound myosin head. According to this hypothesis, the working stroke is much faster than attachment or detachment, but can be observed directly in the rapid force transients that follow step displacement of the filaments. Although many studies of the mechanism of muscle contraction have been based on this hypothesis, the alternative view-that the fast force transients are caused by fast components of attachment and detachment--has not been excluded definitively. Here we show that measurements of the axial motions of the myosin heads at ?ngstr?m resolution by a new X-ray interference technique rule out the rapid attachment/detachment hypothesis, and provide compelling support for the working stroke model of force generation.     

Brain damage: neglect disrupts the mental number line

A popular metaphor for the representation of numbers in the brain is the 'mental number line', in which numbers are represented in a continuous, quantity-based analogical format. Here we show that patients with hemispatial neglect misplace the midpoint of a numerical interval when asked to bisect it (for example, stating that five is halfway between two and six), with an error pattern that closely resembles the bisection of physical lines. This new form of representational neglect constitutes strong evidence that the mental number line is more than simply a metaphor, and that its spatial nature renders it functionally isomorphic to physical lines.     

Screening inhibitors of anthrax lethal factor

The disease anthrax is caused by lethal factor, an enzyme component of the toxin produced by the spore-forming bacterium Bacillus anthracis. Here we describe substrate molecules for this factor that offer a means for high-throughput screening of potential inhibitors for use in anthrax treatment. Our assay should help to answer the urgent call for new and specific therapies to combat this pathogen after its recent emergence as a terrorist bioweapon.     

Direct observation of ligand recognition by T cells

The activation of T cells through interaction of their T-cell receptors with antigenic peptide bound to major histocompatibility complex (MHC) on the surface of antigen presenting cells (APCs) is a crucial step in adaptive immunity. Here we use three-dimensional fluorescence microscopy to visualize individual peptide-I-E(k) class II MHC complexes labelled with the phycobiliprotein phycoerythrin in an effort to characterize T-cell sensitivity and the requirements for forming an immunological synapse in single cells. We show that T cells expressing the CD4 antigen respond with transient calcium signalling to even a single agonist peptide-MHC ligand, and that the organization of molecules in the contact zone of the T cell and APC takes on the characteristics of an immunological synapse when only about ten agonists are present. This sensitivity is highly dependent on CD4, because blocking this molecule with antibodies renders T cells unable to detect less than about 30 ligands.     

Prolactin and growth hormone releasing activity of [D-Met2, Pro5]-enkephalinamide in the rat after systemic administration

Summary The growth hormone (GH) and prolactin releasing (PRL) activity of [D-Met², Pro⁵]-enkephalinamide (EKNH₂), an opioid peptide analog with higher opiate agonist activity that morphine, was compared in the unanesthetized male rat to those of equimolar doses of morphine upon systemic injection. EKNH₂ proved to be a higher PRL, but not GH, releaser than the opiate alkaloid.     

Haemoglobin F intalassemia minor. amino-acid composition

Riassunto Dal sangue di un soggetto affetto daTalassemiaMinor si sono ottenuti cristalli tipici di Hb F.L'analisi della composizione in aminoacidi di tali cristalli porta a concludere che la frazione di Hb alcaliresistente presente in questa malattia e l'Hb F sono identiche.     

An endocannabinoid mechanism for stress-induced analgesia

Acute stress suppresses pain by activating brain pathways that engage opioid or non-opioid mechanisms. Here we show that an opioid-independent form of this phenomenon, termed stress-induced analgesia, is mediated by the release of endogenous marijuana-like (cannabinoid) compounds in the brain. Blockade of cannabinoid CB(1) receptors in the periaqueductal grey matter of the midbrain prevents non-opioid stress-induced analgesia. In this region, stress elicits the rapid formation of two endogenous cannabinoids, the lipids 2-arachidonoylglycerol (2-AG) and anandamide. A newly developed inhibitor of the 2-AG-deactivating enzyme, monoacylglycerol lipase, selectively increases 2-AG concentrations and, when injected into the periaqueductal grey matter, enhances stress-induced analgesia in a CB1-dependent manner. Inhibitors of the anandamide-deactivating enzyme fatty-acid amide hydrolase, which selectively elevate anandamide concentrations, exert similar effects. Our results indicate that the coordinated release of 2-AG and anandamide in the periaqueductal grey matter might mediate opioid-independent stress-induced analgesia. These studies also identify monoacylglycerol lipase as a previously unrecognized therapeutic target.