Structures of five mutants of toxic shock syndrome toxin-1 with reduced biological activity

The three-dimensional structures of five mutants of toxic shock syndrome toxin-1 (TSST-1) have been determined. These mutations are in the long central alpha helix and are useful in mapping portions of TSST-1 involved in superantigenicity and lethality. The T128A, H135A, Q139K, and I140T mutations appear to reduce superantigenicity by altering the properties of the T-cell receptor interaction surface. The Q136A mutation is at a largely buried site and causes a dramatic change in the conformation of the beta7-beta9 loop which covers the back of the central alpha helix. As this mutation has the unique ability to reduce the toxin's lethality in rabbits while retaining its superantigenicity, it raises the possibility that this rear loop mediates the ability of TSST-1 to induce lethality and suggests a route for producing nonlethal toxins for therapeutic development.     

Impact energy measurement in time-of-flight mass spectrometry with cryogenic microcalorimeters

Time-of-flight mass spectrometry-most notably matrix-assisted laser-desorption-ionization time-of-flight (MALDI-TOF) spectrometry-is an important class of techniques for the study of proteins and other biomolecules. Although these techniques provide excellent performance for masses up to about 20,000 daltons, there has been limited success in achieving good mass resolution at higher masses. This is because the sensitivity of the microchannel plate (MCP) detectors used in most systems decreases rapidly with increasing particle mass, limiting the utility of MCP detectors for very large masses. It has recently been proposed that cryogenic particle detectors may provide a solution to these difficulties. Cryogenic detectors measure the thermal energy deposited by the particle impact, and thus have a sensitivity that is largely independent of particle mass. Recent experiments have demonstrated the sensitivity of cryogenic particle detectors to single biomolecules, a quantum efficiency several orders of magnitude larger than the MCP detectors, and sensitivity to masses as large as 750,000 daltons. Here we present results demonstrating an order of magnitude better energy resolution than previous measurements, allowing direct determination of particle charge state during acceleration. Although application of these detectors to practical mass spectrometry will require further development of the detectors and cryogenics, these detectors can be used to elucidate the performance-limiting processes that occur in such systems.     

Different risks of thrombosis in four coagulation defects associated with inherited thrombophilia: a study of 150 families

Deficiency of the naturally occurring anticoagulant proteins, such as antithrombin, protein C and protein S, and activated protein C resistance due to the factor V Leiden gene mutation is associated with inherited thrombophilia. So far, no direct comparison of the thrombotic risk associated with these genetic defects is available. In this study, we wish to compare the lifetime probability of developing thrombosis, the type of thrombotic symptoms, and the role of circumstantial triggering factors in 723 first- and second-degree relatives of 150 index patients with different thrombophilic defects. We found higher risks for thrombosis for subjects with antithrombin (risk ratio 8.1, 95% confidence interval [CI], 3.4 to 19.6), protein C (7.3, 95% CI, 2.9 to 18.4) or protein S deficiency (8.5, 95% CI, 3. 5 to 20.8), and factor V Leiden (2.2, 95% CI, 1.1 to 4.7) than for individuals with normal coagulation. The risk of thrombosis for subjects with factor V Leiden was lower than that for those with all three other coagulation defects (0.3, 95% CI, 0.1 to 1.6), even when arterial and superficial vein thromboses were excluded and the analysis was restricted to deep vein thrombosis (0.3, 95% CI, 0.2 to 0.5). No association between coagulation defects and arterial thrombosis was found. The most frequent venous thrombotic manifestation was deep vein thrombosis with or without pulmonary embolism (90% in antithrombin, 88% in protein C, 100% in protein S deficiency, and 57% in factor V Leiden), but a relatively mild manifestation such as superficial vein thrombosis was common in factor V Leiden (43%). There was a predisposing factor at the time of venous thromboembolism in approximately 50% of cases for each of the four defects. In conclusion, factor V Leiden is associated with a relatively small risk of thrombosis, lower than that for antithrombin, protein C, or protein S deficiency. In addition, individuals with factor V Leiden develop less severe thrombotic manifestations, such as superficial vein thrombosis.     

Preparation and antimicrobial assessment of 2-thioether-linked quinolonyl-carbapenems

This reports the synthesis and in vitro antimicrobial properties of a series of 2-thioether-linked quinolonyl-carbapenems. Although the title compounds exhibited broad spectrum activity, the MICs were generally higher than those observed for selected benchmark carbapenems, quinolonyl-penems, and quinolones. Enzyme assays suggested that the title compounds are potent inhibitors of penicillin binding proteins and inefficient inhibitors of bacterial DNA-gyrase. Uptake studies indicated that the new compounds are not substrates for the norA encoded quinolone efflux pump.