A stochastic model of active zone material mediated synaptic vesicle docking and priming at resting active zones

AbstractSynaptic vesicles (SVs) fuse with the presynaptic membrane (PM) at specialized regions called active zones for synaptic transmission. SVs are associated with dense aggregates of macromolecules called active zone material (AZM) that has been thought to be involved in SV release. However, its role has recently begun to be elucidated. Several morphological studies proposed distinctively different AZM mediated SV docking and priming models: sequential and concurrent SV docking/priming. To explore ways to reconcile the contradictory models we develop a stochastic AZM mediated SV docking and priming model. We assume that the position of each connection site of the AZM macromolecules on their SV, directly linking the SV with the PM, varies by random shortening and lengthening of the macromolecules at resting active zones. We also perform computer simulations of SVs near the PM at resting active zones, and the results show that the distribution of the AZM connection sites can significantly affect the SV’s docking efficiency and distribution of its contact area with the PM, thus priming and that the area correlates with the shape of the SVs providing a way to account for seemingly irreconcilable observations reported about the spatial relationship of SVs with the PM at active zones.</jats:p

Association of factor XIII Val34Leu polymorphism and coronary artery disease: A meta-analysis

Background: Factor XIII plays an important role in the stabilization of the linkage between fibrins and in the pathophysiology of coronary artery disease (CAD). The association between factor XIII Val34Leu polymorphism and CAD risk remains controversial. Methods: We conducted a meta-analysis of 36 studies involving 26,940 cases and 34,694 controls. Subgroup analyses were performed with division of data into disease (myocardial infarction [MI], CAD without MI), age, and sex. Results: Factor XIII Val34Leu polymorphism was significantly associated with ove all CAD risk (odds ratio [OR] = 1.09, 95% confidence interval [CI] = 1.03–1.06, p = 0.004) and MI risk (OR = 1.15, 95% CI 1.07–1.25, p = 0.0003), but not with CAD without MI risk (OR = 1.00, 95% CI 0.87–1.15, p = 0.96). In the subgroup analysis by age and sex, there was no association between Val34Leu polymorphism and CAD. Conclusions: This meta-analysis found that factor XIII Val34Leu polymorphism was associated with CAD risk, especially MI, but not with CAD without MI. In addition, age and sex did not affect the relationship between factor XIII Val34Leu polymorphism and CAD risk.

Scale growth of structures in the turbulent boundary layer with a rod-roughened wall

Direct numerical simulation of a turbulent boundary layer over a rod-roughened wall is performed with a long streamwise domain to examine the streamwise-scale growth mechanism of streamwise velocity fluctuating structures in the presence of two-dimensional (2-D) surface roughness. An instantaneous analysis shows that there is a slightly larger population of long structures with a small helix angle (spanwise inclinations relative to streamwise) and a large spanwise width over the rough-wall compared to that over a smooth-wall. Further inspection of time-evolving instantaneous fields clearly exhibits that adjacent long structures combine to form a longer structure through a spanwise merging process over the rough-wall; moreover, spanwise merging for streamwise scale growth is expected to occur frequently over the rough-wall due to the large spanwise scales generated by the 2-D roughness. Finally, we examine the influence of a large width and a small helix angle of the structures over the rough-wall with regard to spatial two-point correlation. The results show that these factors can increase the streamwise coherence of the structures in a statistical sense.open

Theory of magnetic field-induced metaelectric critical end point in BiMn2_2O5_5

A recent experiment on the multiferroic BiMn$_2$O$_5$ compound under a strong applied magnetic field revealed a rich phase diagram driven by the coupling of magnetic and charge (dipolar) degrees of freedom. Based on the exchange-striction mechanism, we propose here a theoretical model with the intent to capture the interplay of the spin and dipolar moments in the presence of a magnetic field in BiMn$_2$O$_5$. Experimentally observed behavior of the dielectric constants, magnetic susceptibility, and the polarization is, for the most part, reproduced by our model. The critical behavior observed near the polarization reversal $(P=0)$ point in the phase diagram is interpreted as arising from the proximity to the critical end point.Comment: Theory; relevant experiment uploaded as arXiv:0810.190

Cloning and high-level production of a chitinase from Chromobacterium sp. and the role of conserved or nonconserved residues on its catalytic activity

A gene encoding an alkaline (pI of 8.67) chitinase was cloned and sequenced from Chromobacterium sp. strain C-61. The gene was composed of 1,611 nucleotides and encoded a signal sequence of 26N-terminal amino acids and a mature protein of 510 amino acids. Two chitinases of 54 and 52kDa from both recombinant Escherichia coli and C-61 were detected on SDS-PAGE. Maximum chitinase activity was obtained in the culture supernatant of recombinant E. coli when cultivated in TB medium for 6days at 37°C and was about fourfold higher than that from C-61. Chi54 from the culture supernatants could be purified by a single step based on isoelectric point. The purified Chi54 had about twofold higher binding affinity to chitin than to cellulose. The chi54 encoded a protein that included a type 3 chitin-binding domain belonging to group A and a family 18 catalytic domain belonging to subfamily A. In the catalytic domain, mutation of perfectly conserved residues and highly conserved residues resulted in loss of nearly all activity, while mutation of nonconserved residues resulted in enzymes that retained activity. In this process, a mutant (T218S) was obtained that had about 133% of the activity of the wild type, based on comparison of K cat value