Catalysis of creatine kinase refolding by protein disulfide isomerase involves disulfide cross-link and dimer to tetramer switch

Protein disulfide isomerase (PDI) functions as an isomerase to catalyze thiol:disulfide exchange, as a chaperone to assist protein folding, and as a subunit of prolyl-4-hydroxylase and microsomal triglyceride transfer protein. At a lower concentration of 0.2 microm, PDI facilitated the aggregation of unfolded rabbit muscle creatine kinase (CK) and exhibited anti-chaperone activity, which was shown to be mainly due to the hydrophobic interactions between PDI and CK and was independent of the cross-linking of disulfide bonds. At concentrations above 1 microm, PDI acted as a protector against aggregation but an inhibitor of reactivation during CK refolding. The inhibition effect of PDI on CK reactivation was further characterized as due to the formation of PDI-CK complexes through intermolecular disulfide bonds, a process involving Cys-36 and Cys-295 of PDI. Two disulfide-linked complexes containing both PDI and CK were obtained, and the large, soluble aggregates around 400 kDa were composed of 1 molecule of tetrameric PDI and 2 molecules of inactive intermediate dimeric CK, whereas the smaller one, around 200 kDa, was formed by 1 dimeric PDI and 1 dimeric CK. To our knowledge this is the first study revealing that PDI could switch its conformation from dimer to tetramer in its functions as a foldase. According to the observations in this research and our previous study of the folding pathways of CK, a working model was proposed for the molecular mechanism of CK refolding catalyzed by PDI.     

SSR alpha and associated calnexin are major calcium binding proteins of the endoplasmic reticulum membrane

GTP phosphorylation of rough microsomes in vitro is limited to four integral membrane proteins. Two of these, a phosphoprotein (pp90) and a phosphoglycoprotein (pgp35) were purified as a complex with two nonphosphorylated membrane glycoproteins, gp25H and gp25L. The authenticity of this complex was confirmed using two different purification procedures and by coimmunoprecipitation. By immunofluorescence a reticulated cytoplasmic network was revealed for the proteins which was similar to that for Louvard et al. (Louvard, D., Reggio, H., and Warren, G. (1982) J. Cell Biol. 92, 92-107) marker antisera which also recognized purified pp90 on immunoblots. Amino acid sequencing of peptides derived from pgp35 identified this protein as SSR alpha, an endoplasmic reticulum constituent as identified by cross-linking of translocating nascent chains (G?rlich, D, Prehn, S., Hartmann, E., Herz, J., Otto, A., Kraft, R., Wiedmann, M., Knespel, S., Dobberstein, B., and Rapoport, T. A. (1990) J. Cell Biol. 111, 2283-2294). The sequence of gp25H was determined from cDNA clones and was identical with SSR beta identified by G?rlich et al. (1990) as being tightly bound to SSR alpha. Sequencing of gp25L revealed no similarity of the deduced sequence with other proteins. However, pp90 revealed a high degree of sequence identity with the Ca(2+)-binding protein, calreticulin. 45Ca2+ overlay studies indicated that pp90 bound Ca2+ and the name calnexin is proposed. Surprisingly, pgp25 (SSR alpha) also bound Ca2+ although gp25H (SSR beta) and gp25L did not. Triton X-114 partitioning of the integral membrane proteins of rough microsomes suggested that pgp35 (SSR alpha) and calnexin were major Ca(2+)-binding proteins of the endoplasmic reticulum membrane. We propose that the function of the complex is to regulate Ca(2+)-dependent retention mechanisms for luminal proteins of the endoplasmic reticulum.     

猪链球菌2型国内分离株毒力相关蛋白的分析

提纯猪链球菌 2型江苏分离株HA980 1的毒力相关蛋白溶菌酶释放蛋白 (muramini dase releasedprotein ,MRP)和胞外因子 (extracellularfacter,EF) ,制备其抗体供免疫转印之用。另提取猪源链球菌 1 7株国内分离株、1株德国分离株及 1株猪链球菌 2型人分离株的胞壁和胞外蛋白 ,经SDS PAGE ,与HA980 1株的MRP和EF的抗体作免疫转印。 1 1株MRP阳性 ,1 0株EF及EF 阳性 ,MRP及EF的分布存在 4种表型 :MPR+ EF+ (8 1 9) ,MRP+ EF (1 1 9) ,MRP+ EF- (1 1 9) ,MRP- EF- (1 0 1 9)。     

Nuclear factor-κB signaling pathway is involved in phospholipase Cε-regulated proliferation in human renal cell carcinoma cells

Glioblastoma is the most aggressive cerebral gliomas. Despite advances in therapies, the prognosis is still very poor. Therefore, novel therapeutic strategies are required. As a proteasome inhibitor, bortezomib has shown its efficacy as an active antitumor agent against a variety of tumors. However, inhibition of proteasome activity leads to cell death and also induces cell autophagy, and due to the dual roles of autophagy in the survival and death of tumor cells, the effect of inhibition of autophagy on glioblastoma cells remains to be explored. We therefore assessed whether bortezomib is capable of inducing autophagy, and investigated the antitumor effect of bortezomib combined with autophagy inhibitors on human glioblastoma U251 and U87 cells. Cell viability was measured by MTT assay. The expressions of autophagy and apoptosis-related proteins were determined by Western blot analysis. U251 and U87 cells proliferation was inhibited in a dose-dependent manner. Both apoptosis and autophagy induced by bortezomib were observed in human glioblastoma U87 and U251 cells. However, when U251 and U87 cells were co-treated with bortezomib and autophagy inhibitors 3-MA or Atg7 siRNA, the autophagy inhibitors blocked the autophagy in the cells and resulted in a further inhibition of cell proliferation and a further increase in cell apoptosis as compared with that treated with bortezomib alone. These findings indicated that combination of bortezomib and autophagy inhibitors may shed new light on glioblastoma treatment.     

Identification of New Genetic Risk Variants for Type 2 Diabetes

Although more than 20 genetic susceptibility loci have been reported for type 2 diabetes (T2D), most reported variants have small to moderate effects and account for only a small proportion of the heritability of T2D, suggesting that the majority of inter-person genetic variation in this disease remains to be determined. We conducted a multistage, genome-wide association study (GWAS) within the Asian Consortium of Diabetes to search for T2D susceptibility markers. From 590,887 SNPs genotyped in 1,019 T2D cases and 1,710 controls selected from Chinese women in Shanghai, we selected the top 2,100 SNPs that were not in linkage disequilibrium (r²<0.2) with known T2D loci for in silico replication in three T2D GWAS conducted among European Americans, Koreans, and Singapore Chinese. The 5 most promising SNPs were genotyped in an independent set of 1,645 cases and 1,649 controls from Shanghai, and 4 of them were further genotyped in 1,487 cases and 3,316 controls from 2 additional Chinese studies. Consistent associations across all studies were found for rs1359790 (13q31.1), rs10906115 (10p13), and rs1436955 (15q22.2) with P-values (per allele OR, 95%CI) of 6.49×10⁻⁹ (1.15, 1.10–1.20), 1.45×10⁻⁸ (1.13, 1.08–1.18), and 7.14×10⁻⁷ (1.13, 1.08–1.19), respectively, in combined analyses of 9,794 cases and 14,615 controls. Our study provides strong evidence for a novel T2D susceptibility locus at 13q31.1 and the presence of new independent risk variants near regions (10p13 and 15q22.2) reported by previous GWAS.     

Chaperone-like activity of peptidyl-prolyl cis-trans isomerase during creatine kinase refolding

Porcine kidney 18 kD peptidyl-prolyl cis-trans isomerase (PPIase) belongs to the cyclophilin family that is inhibited by the immunosuppressive drug cyclosporin A. The chaperone activity of PPIase was studied using inactive, active, and alkylated PPIase during rabbit muscle creatine kinase (CK) refolding. The results showed that low concentration inactive or active PPIase was able to improve the refolding yields, while high concentration PPIase decreased the CK reactivation yields. Aggregation was inhibited by inactive or active PPIase, and completely suppressed at 32 or 80 times the CK concentration (2.7 microM). However, alkylated PPIase was not able to prevent CK aggregation. In addition, the ability of inactive PPIase to affect CK reactivation and prevent CK aggregation was weaker than that of active PPIase. These results indicate that PPIase interacted with the early folding intermediates of CK, thus preventing their aggregation in a concentration-dependent manner. PPIase exhibited chaperone-like activity during CK refolding. The results also suggest that the isomerase activity of PPIase was independent of the chaperone activity, and that the proper molar ratio was important for the chaperone activity of PPIase. The cysteine residues of PPIase may be a peptide binding site, and may be an essential group for the chaperone function.     

Effects of polysaccharides from <Emphasis Type="Italic">Morchella conica</Emphasis> on nitric oxide production in lipopolysaccharide-treated macrophages

Morchella conica is a species of rare edible mushroom whose multiple medicinal functions have been proven. However, reports barely mention the mechanisms of these functions. In this study, the effects of two polysaccharides from M. conica (PMCs) on nitric oxide (NO) production in lipopolysaccharide (LPS)-treated macrophages were investigated. The results showed that 50–200 μg/ml of the extracellular polysaccharide (EPMC) and 25–200 μg/ml of the intracellular polysaccharide (IPMC) significantly inhibited NO production. Accordingly, the signal mechanisms were also explored. It was found that 100 μg/ml of EPMC and 25 μg/ml of IPMC could efficiently down-regulate the inducible nitric oxide synthase (iNOS) expression and nuclear factor-κB (NF-κB) DNA-binding activity and up-regulate heme oxygenase 1 (HO-1) expression. Moreover, by using a HO-1 inhibitor NaPP to treat the cells, the PMC-inhibited NO production and iNOS expression, rather than NF-κB activation, were released partially, indicating that HO-1 probably medicates the inhibition of PMCs on iNOS and NO. Besides, EPMC also significantly suppressed the phosphorylation of p38 mitogen-activated protein kinase (p38), c-jun N-terminal kinase, mitogen-activated protein kinase kinase 4, and expression of NF-κB inducing kinase, while IPMC seemed to show no regular effect on p38. In conclusion, PMCs inhibited NO production in LPS-induced macrophages through regulating a series of signal pathways, suggesting that PMCs play a potential role on immunomodulation and treating related diseases.     

吴茱萸五加紫丁香甙含量分析

吴茱萸五加（Acauthopanax evodiaefodius Franch.)在我国南方各省分布较广,资源较丰富,为寻求新的药物资源,用反相高效液相色谱法对吴茱萸五加的化学成分进行了分析,发现其紫丁香甙含量较多,紫丁香甙药用价值较高,本分析方法分离效果好,简便,快速,准确度和精密度高,相对标准偏差为1．8％,平均回收率为98．4％。