Shear‐induced unfolding activates von Willebrand factor A2 domain for proteolysis

Summary. Background: To avoid pathological platelet aggregation by von Willebrand factor (VWF), VWF multimers are regulated in size and reactivity for adhesion by ADAMTS13‐mediated proteolysis in a shear flow dependent manner. Objective and methods: We examined whether tensile stress in VWF under shear flow activates the VWF A2 domain for cleavage by ADAMTS13 using molecular dynamics simulations. We generated a full length mutant VWF featuring a homologous disulfide bond in A2 (N1493C and C1670S), in an attempt to lock A2 against unfolding. Results: We indeed observed stepwise unfolding of A2 and exposure of its deeply buried ADAMTS13 cleavage site. Interestingly, disulfide bonds in the adjacent and highly homologous VWF A1 and A3 domains obstruct their mechanical unfolding. We find this mutant A2 (N1493C and C1670S) to feature ADAMTS13‐resistant behavior in vitro. Conclusions: Our results yield molecular‐detail evidence for the force‐sensing function of VWF A2, by revealing how tension in VWF due to shear flow selectively exposes the A2 proteolysis site to ADAMTS13 for cleavage while keeping the folded remainder of A2 intact and functional. We find the unconventional ‘knotted’ Rossmann fold of A2 to be the key to this mechanical response, tailored for regulating VWF size and activity. Based on our model we discuss the pathomechanism of some natural mutations in the VWF A2 domain that significantly increase the cleavage by ADAMTS13 without shearing or chemical denaturation, and provide with the cleavage‐activated A2 conformation a structural basis for the design of inhibitors for VWF type 2 diseases.     

A simulation based technique to estimate intracluster correlation for a binary variable

Cluster randomized trials have become the design of choice for evaluating the effect of selected interventions on well-known health indicators such as neonatal mortality rate, episiotomy rate, and postpartum hemorrhage rate in a community setting. Determining the sample size of a cluster randomized trial requires a reliable estimate of cluster size and the intracluster correlation (ICC), because sample size can be substantially impacted by these parameters. During the design phase of a trial, the investigators may have estimates of the valid range of the health indicator which is the primary outcome variable. Furthermore, investigators often have an estimate of the average cluster size or range of cluster sizes that exist among the proposed samples they are planning to include in the trial. We present in this article a simulation technique to estimate the ICC value and its distribution for known binary outcome variables and a varying number of clusters and cluster sizes. We applied this technique to estimate ICC values and confidence intervals for a multi-country trial assessing the effect of neonatal resuscitation to decrease seven-day neonatal mortality, where communities within a country were clusters. This simulation technique can be used to estimate the possible ranges of the ICC values and to help to design an appropriately powered trial.     

祛白酊质量标准的实验研究

目的：建立祛白酊的质量标准。方法：采用薄层色谱法鉴别其中的补骨脂素,异补骨脂素,栀子苷;导数分光光度法测定其中醋酸氢化可的松的含量。结果;薄层色谱鉴别方法有良好的重现性,专属性;醋酸氢化可的松在11－19ug.ml^-1呈良好的线性关系（r=0.9996)其含量测定平均回收率100．9％,RSD＝0．9％（n=5)。结论：制定的质量标准可以保证祛白酊的质量。     

培养心肌细胞牵张刺激装置的建立及应用

1　方法　牵张刺激装置的制作如模式图 1.制作实验模型采用材料为有机玻璃板、2 4孔培养板、硅胶膜 (厚度 0 .2 2 μｍ) .硅胶膜从平面圆形变为球形时 ,面积扩大的百分比 =(Ｓ球 -Ｓ园 ) /Ｓ园 ,其中Ｓ球 =ＡＤ2 ,Ｓ园 =ｒ2 ,而ＡＤ2 =ｈ2 +ｒ2 ,其中ｒ为孔的半径 ,ｈ为膜升高的高度图 2 .通过控制ｈ的大小 ,可控制膜被牵拉的强度 .本实验采用使膜面积扩大 2 0 %的强度 ,故ｈ =4ｍｍ[1] .参照Ｋａｓｓｉｒｉ等[2 ,3 ] 方法进行心肌细胞的分离培养 .生长有贴壁心肌细胞的 2 4孔板被固定于牵张装置 ,缓慢充气使硅胶膜向上凸起 4ｍｍ ,分别维持…     

Comparison of the urine-based ligase chain reaction test to culture for detection of Chlamydia trachomatis and Neisseria gonorrhoeae in pediatric sexual abuse victims

BACKGROUND: The urine-based ligase chain reaction (LCR) assay for Chlamydia trachomatis and Neisseria gonorrhoeae is an attractive alternative to culture because of the relative ease with which specimens may be collected, transported and processed. In addition LCR offers superior sensitivity while maintaining high specificity when compared with culture in various studies of adolescents and adults. A study comparing LCR to culture has not been published concerning children. METHODS: We conducted a prospective, comparison trial of the urine-based LCR test for Chlamydia trachomatis and Neisseria gonorrhoeae as compared with culture among children at a specialized referral center for evaluation for alleged sexual assault. Of the 1,010 children presenting to the center during the study period, 164 met the study requirements for risk of a sexually transmissible disease and collection of both culture and urine LCR specimens. RESULTS: Eight specimens tested positive by both methods for C. trachomatis. Another 10 specimens tested positive for C. trachomatis by LCR but were negative by culture. No patient with a negative LCR for C. trachomatis had a positive culture. For N. gonorrhoeae 2 specimens tested positive by both methods, and 3 specimens tested positive by LCR but negative by culture. No patient with a negative LCR for N. gonorrhoeae had a positive culture. CONCLUSIONS: The low prevalence of disease in the study population precluded statistical analysis. LCR may prove to be as specific and more sensitive than culture for the detection of C. trachomatis and N. gonorrhoeae in children. Further studies are needed.     

Complex orofacial movements and the disappearance of cerebellar mutism: report of five cases

A syndrome of mutism and subsequent dysarthria occurs frequently in children after resection of a cerebellar tumour. The role of orofacial and speech motor control in this syndrome has not been studied systematically. We examined simple and complex orofacial movements during the mute phase and shortly after the resumption of speech in five children with mutism and subsequent dysarthria. The recovery of complex orofacial movements coincided with the disappearance of the mutism     

Interleukin-5 is at 5q31 and is deleted in the 5q- syndrome

Human interleukin-5 (IL-5) is a selective eosinophilopoietic and eosinophil-activating growth hormone. By in situ hybridization this gene is mapped to chromosome 5q23.3 to 5q32. It is shown to be deleted in two patients with the 5q-syndrome and in one patient previously diagnosed with myelodysplasia whose condition had progressed to acute myeloblastic leukemia. The clustering of other genes involved in hematopoiesis (IL-3, granulocyte-macrophage colony-stimulating factor, feline sarcoma viral oncogene homolog, colony-stimulating factor 1) to the same region as IL-5 suggests a nonrandom localization and raises interesting questions concerning the evolution and regulation of these genes.