Specificity of signal peptide recognition in tat-dependent bacterial protein translocation

The bacterial twin arginine translocation (Tat) pathway translocates across the cytoplasmic membrane folded proteins which, in most cases, contain a tightly bound cofactor. Specific amino-terminal signal peptides that exhibit a conserved amino acid consensus motif, S/T-R-R-X-F-L-K, direct these proteins to the Tat translocon. The glucose-fructose oxidoreductase (GFOR) of Zymomonas mobilis is a periplasmic enzyme with tightly bound NADP as a cofactor. It is synthesized as a cytoplasmic precursor with an amino-terminal signal peptide that shows all of the characteristics of a typical twin arginine signal peptide. However, GFOR is not exported to the periplasm when expressed in the heterologous host Escherichia coli, and enzymatically active pre-GFOR is found in the cytoplasm. A precise replacement of the pre-GFOR signal peptide by an authentic E. coli Tat signal peptide, which is derived from pre-trimethylamine N-oxide (TMAO) reductase (TorA), allowed export of GFOR, together with its bound cofactor, to the E. coli periplasm. This export was inhibited by carbonyl cyanide m-chlorophenylhydrazone, but not by sodium azide, and was blocked in E. coli tatC and tatAE mutant strains, showing that membrane translocation of the TorA-GFOR fusion protein occurred via the Tat pathway and not via the Sec pathway. Furthermore, tight cofactor binding (and therefore correct folding) was found to be a prerequisite for proper translocation of the fusion protein. These results strongly suggest that Tat signal peptides are not universally recognized by different Tat translocases, implying that the signal peptides of Tat-dependent precursor proteins are optimally adapted only to their cognate export apparatus. Such a situation is in marked contrast to the situation that is known to exist for Sec-dependent protein translocation.     

A two-muscle,continuum-mechanical forward simulation of the upper limb

By following the common definition of forward-dynamics simulations, i.e. predicting movement based on (neural) muscle activity, this work describes, for the first time, a forward-dynamics simulation framework of a musculoskeletal system, in which all components are represented as continuous, three-dimensional, volumetric objects. Within this framework, the mechanical behaviour of the entire muscle–tendon complex is modelled as a nonlinear hyperelastic material undergoing finite deformations. The feasibility and the full potential of the proposed forward-dynamics simulation framework is demonstrated on a two-muscle, three-dimensional, continuum-mechanical model of the upper limb. The musculoskeletal model consists of three bones, i.e. humerus, ulna, and radius, an one-degree-of-freedom elbow joint, and an antagonistic muscle pair, i.e. the biceps and triceps brachii, and takes into consideration the contact between the skeletal muscles and the humerus. Numerical studies have shown that the proposed upper limb model is capable of predicting realistic moment arms and muscle forces for the entire range of activation and motion. Within the limitations of the model, the presented simulations provide, for the first time, insights into existing contact forces and their influence on the muscle fibre stretch. Based on the presented simulations, the overall change in fibre stretch is typically less than 3%, despite the fact that the contact forces reach up to 71% of the exerted muscle force. Movement-predicting simulations are achieved by minimising a nonlinear moment equilibrium equation. Based on the forward-dynamics simulation approach, an iterative solution procedures for position-driven (inverse dynamics) and force-driven scenarios have been proposed accordingly. Applying these methodologies to time-dependent scenarios demonstrates that the proposed methods can be linked to state-of-the-art control algorithms predicting time-dependent muscle activation levels based on principles of forward dynamics.     

Age Effects in L2 Grammar Processing as Revealed by ERPs and How (Not) to Study Them

In this study we investigate the effect of age of acquisition (AoA) on grammatical processing in second language learners as measured by event-related brain potentials (ERPs). We compare a traditional analysis involving the calculation of averages across a certain time window of the ERP waveform, analyzed with categorical groups (early vs. late), with a generalized additive modeling analysis, which allows us to take into account the full range of variability in both AoA and time. Sixty-six Slavic advanced learners of German listened to German sentences with correct and incorrect use of non-finite verbs and grammatical gender agreement. We show that the ERP signal depends on the AoA of the learner, as well as on the regularity of the structure under investigation. For gender agreement, a gradual change in processing strategies can be shown that varies by AoA, with younger learners showing a P600 and older learners showing a posterior negativity. For verb agreement, all learners show a P600 effect, irrespective of AoA. Based on their behavioral responses in an offline grammaticality judgment task, we argue that the late learners resort to computationally less efficient processing strategies when confronted with (lexically determined) syntactic constructions different from the L1. In addition, this study highlights the insights the explicit focus on the time course of the ERP signal in our analysis framework can offer compared to the traditional analysis.     

Meteorological Influences on the Incidence of Aneurysmal Subarachnoid Hemorrhage – A Single Center Study of 511 Patients

Objective

To assess the potential meteorological influence on the incidence of aneurysmal subarachnoid hemorrhage (SAH). Previous studies used inhomogeneous patient groups, insufficient study periods or inappropriate statistics.

Patients and Methods

We analyzed 511 SAH admissions between 2004 and 2012 for which aneurysmal rupture occurred within the Zurich region. The hourly meteorological parameters considered are: surface pressure, 2-m temperature, relative humidity and wind gusts, sunshine, and precipitation. For all parameters we investigate three complementary statistical measures: i) the time evolution from 5 days before to 5 days after the SAH occurrence; ii) the deviation from the 10-year monthly mean; and iii) the change relative to the parameter''s value two days before SAH occurrence. The statistical significance of the results is determined using a Monte Carlo simulation combined with a re-sampling technique (1000×).

Results

Regarding the meteorological parameters considered, no statistically significant signal could be found. The distributions of deviations relative to the climatology and of the changes during the two days prior to SAH events agree with the distributions for the randomly chosen days. The analysis was repeated separately for winter and summer to exclude compensating effects between the seasons.

Conclusion

By using high-quality meteorological data analyzed with a sophisticated and robust statistical method no clearly identifiable meteorological influence for the SAH events considered can be found. Further studies on the influence of the investigated parameters on SAH incidence seem redundant.     

A conserved cysteine is essential for Pex4p-dependent ubiquitination of the peroxisomal import receptor Pex5p

The peroxisomal protein import receptor Pex5p is modified by ubiquitin, both in an Ubc4p-dependent and -independent manner. Here we show that the two types of ubiquitination target different residues in the NH(2)-terminal region of Pex5p and we identify Pex4p (Ubc10p) as the ubiquitin-conjugating enzyme required for Ubc4p-independent ubiquitination. Whereas Ubc4p-dependent ubiquitination occurs on two lysine residues, Pex4p-dependent ubiquitination neither requires lysine residues nor the NH(2)-terminal alpha-NH(2) group. Instead, a conserved cysteine residue appears to be essential for both the Pex4p-dependent ubiquitination and the overall function of Pex5p. In addition, we show that this form of ubiquitinated Pex5p is susceptible to the reducing agent beta-mercaptoethanol, a compound that is unable to break ubiquitin-NH(2) group linkages. Together, our results strongly suggest that Pex4p-dependent ubiquitination of Pex5p occurs on a cysteine residue.     

1,5-anhydro-D-fructose from D-fructose

1,5-Anhydro-d-fructose was efficiently prepared from d-fructose via regiospecific 1,5-anhydro ring formation of 2,3-O-isopropylidene-1-O-methyl(tolyl)sulfonyl-d-fructopyranose and subsequent deprotection.     

Natural female mating rate maximizes hatchling size in a marine invertebrate

1. Males and females often differ in their optimal mating rates, resulting potentially in conflicts over remating. In species with separate sexes, females typically have a lower optimal mating rate than males, and can regulate contacts with males accordingly. The realized mating rate may therefore be closer to the female's optimum. In simultaneous hermaphrodites, however, it has been suggested that the intraindividual optimization between 'male' and 'female' interests generates more 'male'-driven mating rates. 2. In order to assess the consequences of variation in mating rate on 'female' reproductive output, we exposed the simultaneously hermaphroditic sea slug Chelidonura sandrana to four mating rate regimes and recorded the effects on a variety of fitness components. 3. In focal 'females', we found (i) a slight but significant linear decrease in fecundity with mating rate, whereas (ii) maternal investment in egg capsule volume peaked at an intermediate mating rate. 4. Combining the observed fecundity cost with the apparent benefits of larger offspring size suggests that total female fitness is maximized at an intermediate mating rate. With the latter being close to the natural mating rate of C. sandrana in the field, our findings challenge the assumption of 'male'-driven mating systems in simultaneous hermaphrodites. 5. Our study provides experimental evidence for various mathematical models in which female fitness is maximized at intermediate mating rates.