肠道病毒71型3C蛋白酶在大肠杆菌中的表达及活性研究

本研究利用大肠杆菌表达系统构建肠道病毒71型3C蛋白酶,并进行纯化,对其酶活性进行研究。首先,将3C蛋白酶基因克隆至pET28a载体,在大肠杆菌BL21(DE3)中表达,Ni-NTA柱亲和层析纯化获得3C蛋白酶,经肠激酶酶切去除N端His标签后获得无His标签的3C蛋白酶,再以荧光多肽为底物进行酶活性研究。经过双酶切鉴定和测序证实,重组表达质粒pET28a-3C构建正确,表达的重组3C蛋白酶相对分子质量约22kD;纯化后有无His标签的3C蛋白酶均能催化荧光底物3B-3C,并且两者的酶动力学数据无显著差异,含有His标签的3C蛋白酶Km、Vmax、Kcat分别为22μM、434nM.Min-1、0.0669 Min-1;其最适反应pH为7.0,最佳反应温度为30℃～37℃。本实验成功表达并纯化了重组3C蛋白酶,该酶具有良好的活力,为抗病毒抑制剂、结构蛋白组装、疫苗开发及3C蛋白酶检测方法的研发奠定了基础。     

Expression and characterization of a novel mesophilic protease from metagenomic library derived from Antarctic coastal sediment

A metagenomic cosmid library was constructed, in which the insert DNA was derived from the coastal sediment near Antarctic China Zhongshan Station. One clone (ACPRO001) expressing protease activity was isolated from the library using milk agar plates. Sequencing of the clone revealed a novel protease gene. The amino acid sequence comparison and phylogenetic analysis indicated that it could be classified as a subtilisin-like serine protease, though the highly conserved residue Asp was replaced by Ala. The ACPRO001 protease gene was expressed in pET-His and purified for characterization. The optimal temperature and pH for the activity of the ACPRO001 protease were 60°C and pH 9.0, respectively. The enzyme retained about 73% of residual activity after 2 h incubation at 50°C in the presence of Ca²⁺. The presence of Ca²⁺ increased the thermostability of ACPRO001 protease obviously. The enzymatic activity was inhibited by 1 mM phenylmethyl sulfonylfluoride (PMSF) and hydrochloride 4-(2-aminoethyl)-benzenesulfonyl fluoride (AEBSF), indicating that it was a serine protease.     

The role of B-cell-specific activator protein in the response of malignant B-1 cells to LPS

Chronic lymphocytic leukemia (CLL) results from the uncontrolled proliferation and accumulation of B-1 cells, many of which demonstrate self-reactivity. The response of B-1 cells to mitogen after undergoing malignant transformation is still unclear. Using our established malignant B-1 cell lines derived from the NZB murine model of human CLL, we investigated the response of malignant B-1 cells to the mitogen LPS. Interestingly, these malignant B-1 cells proliferated initially, but the proliferation rate decreased after a 48-h transition. Prolonged LPS treatment induced apoptosis and pathological differentiation. We studied possible underlying molecular mechanisms and found that the level of the DNA binding protein BSAP (B-cell-specific activator protein) was upregulated by LPS at the initial activation stage, followed by an increase in the apoptotic factor caspase-3 (CPP32) at 48 h and a subsequent decrease of BSAP at 72 h. The pathological differentiation induced by LPS was partially prevented by treatment with antisense BSAP. This study indicates that malignant B-1 cells could be driven to apoptosis and pathological differentiation when activated by the mitogen LPS, and BSAP may be an important factor in regulating these responses.     

Haemophilus influenzae immunoglobulin A1 protease genes: cloning by plasmid integration-excision, comparative analyses, and localization of secretion determinants.

Many bacteria which establish infections after invasion at human mucosal surfaces produce enzymes which cleave immunoglobulin A (IgA), the primary immunoglobulin involved with protection at these sites. Bacterial species such as Haemophilus influenzae which produce IgA1 proteases secrete this enzyme into their environment. However, when the gene encoding this protein was isolated from H. influenzae serotype d and introduced into Escherichia coli, the activity was not secreted into the medium but was localized in the periplasmic space. In this study, the IgA1 protease gene (iga) from an H. influenzae serotype c strain was isolated and the gene from the serotype d strain was reisolated. The IgA1 proteases produced in E. coli from these genes were secreted into the growth medium. A sequence linked to the carboxyl terminus of the iga gene but not present in the original clone was shown to be necessary to achieve normal secretion. Tn5 mutagenesis of the additional carboxyl-terminal region was used to define a 75- to 100-kilodalton coding region required for complete secretion of IgA1 protease but nonessential for protease activity. The iga genes were isolated by a plasmid integration-excision procedure. In this method a derivative of plasmid pBR322 containing a portion of the protease gene and the kanamycin resistance determinant of Tn5 was introduced into H. influenzae by transformation. The kanamycin resistance gene was expressed in H. influenzae, but since pBR322 derivatives are unable to replicate in this organism, kanamycin-resistant transformants arose by integration of the plasmid into the Haemophilus chromosome by homologous recombination. The plasmid, together with the adjoining DNA encoding IgA1 protease, was then excised from the chromosome with DNA restriction enzymes, religated, and reintroduced into E. coli. Comparisons between the H. influenzae protease genes were initiated which are useful in locating functional domains of these enzymes.     

On the possible involvement of bovine serum albumin precursor in lipofection pathway

Protein factors involved in lipofection pathways remain elusive. Using avidin-biotin affinity chromatography and mass finger printing analysis technique, herein we report the identification of a 70 kDa size protein (bovine serum albumin precursor, BSAP) which binds strongly with lipoplexes and may play role in lipofection pathway. Using multiple cultured animal cells and three structurally different cationic transfection lipids, we show that the efficiencies of liposomal transfection vectors get significantly enhanced (by ~2.5- to 5.0-fold) in cells pre-transfected with lipoplexes of reporter plasmid construct encoding BSAP. Findings in the cellular uptake experiments in A549 cells cultured in DMEM supplemented with 10% (w/w) BODIPY-labelled BSAP are consistent with the supposition that BSAP enters cell cytoplasm from the cell culture medium (DMEM supplemented with 10% FBS) used in lipofection. Cellular uptake studies by confocal microscopy using BODIPY-labelled BSAP and FITC-labelled plasmid DNA revealed co-localization of plasmid DNA and BSAP within the cell cytoplasm and nucleus. In summary, the present findings hint at the possible involvement of BSAP in lipofection pathway.     

Substitution mutations of the highly conserved arginine 87 of HIV-1 protease result in loss of proteolytic activity

The 297bp gene coding for the HIV-1 protease was chemically synthesized and expressed in E. coli. Single amino acid substitutions (Arg 87 - greater than Lys; Arg 87 - greater than Glu) were introduced in the C-terminally located conserved region GlyArgAsn of the protease gene in the wild-type clone. The products of the mutant and the wild-type clones were expressed at approximately similar levels at 30 minutes of induction but the mutant protease proteins accumulated as a function of time of induction unlike the wild-type protease which declined after 60 minutes. The mutants were completely devoid of proteolytic activity as determined in assays employing as substrates a synthetic nonapeptide and a gag related recombinant polyprotein.     

Effect of Vitamin D Therapy on Bone Turnover Markers in Postmenopausal Women with Osteoporosis and Osteopenia

ObjectiveTo (7) assess the rate of reduction in bone turnover with vitamin D and bisphosphonate therapies and (2) evaluate the clinical utility of bone-specific alkaline phosphatase (BSAP) in monitoring treatment response.MethodsWe retrospectively reviewed medical records of patients with newly diagnosed osteopenia and osteoporosis from 2002 to 2009 at Loyola University Medical Center. A cohort of postmenopausal women with hip or spine T-scores of less than -1, normal serum creatinine, and no prior vitamin D or bisphosphonate therapy was divided into vitamin D-deficient (n = 29) and vitamin D-sufficient (n = 13) groups. Vitamin D-deficient patients received high-dose vitamin D, whereas vitamin D-sufficient patients received orally administered bisphosphonates. BSAP levels at baseline and 1 year were compared.Resultsvitamin D therapy in the group with vitamin D deficiency led to a 26.7% decrease in BSAP (P < .01). Bisphosphonate therapy in the vitamin D-sufficient group led to a 32.7% decrease in BSAP (P = .01). The magnitude of BSAP change in the 2 study groups (6.74 ± 6.48 μg ∕ L and 8.72 ± 9.94 μgZL) did not differ significantly (P = .45).ConclusionThe results of this study suggest that correction of vitamin D deficiency in patients with osteopenia and osteoporosis can lead to a decrease in bone turnover as measured by BSAP and that the magnitude of this reduction is similar to that achieved with orally administered bisphosphonates. (Endocr Pract. 2011;17:873-879)     

Herpes simplex virus type 1 protease expressed in Escherichia coli exhibits autoprocessing and specific cleavage of the ICP35 assembly protein.

The UL26 gene of herpes simplex virus type 1 (HSV-1) encodes a protease which is responsible for the C-terminal cleavage of the nucleocapsid-associated proteins, ICP35 c and d, to their posttranslationally modified counterparts, ICP35 e and f. To further characterize the HSV-1 protease, the UL26 gene product was expressed in Escherichia coli. The expressed protease underwent autoproteolytic processing at two independent sites. The first site is shared with ICP35 and results in removal of 25 amino acids from the C terminus of the protease. The second unique site gives rise to protein species consistent with deletion of a 28-kDa fragment at the N terminus. A mutant protease, which showed no activity in a mammalian cell cotransfection assay (F. Liu and B. Roizman, Proc. Natl. Acad. Sci. USA 89:2076-2080, 1992), failed to exhibit autoproteolytic processing at either site when expressed in bacteria. The inactive mutant was able to serve as a substrate in a trans assay in which the substrate and protease were coexpressed in bacteria. This experiment demonstrated that the unique N-terminal processing was mediated exclusively by the HSV-1 protease. ICP35 c,d also served as a substrate in this assay and was correctly processed by HSV-1 protease in E. coli. This trans-cleavage assay will aid in the characterization of HSV-1 protease and assist in investigation of the role of proteolytic processing in the virus.     

Characterization of a neutral serine protease and its full-length cDNA from the nematode-trapping fungus Arthrobotrys oligospora

A neutral serine protease (designated Aoz1) was purified to homogeneity from a strain of Arthrobotrys oligospora, obtained from soil in Yunnan Province. The purified protein showed a molecular mass of approximately 38?000 Dalton, pI 4.9 and displayed optimal activity at 45 C and pH 6-8. The protein could hydrolyze gelatin, casein and the chromogenic substrate azocoll, and it could immobilize nematodes in vitro (Panagrellus redivivus L. [Goodey]). The level of activity in culture medium was found to increase with increasing gelatin concentration. Scanning electron micrographs demonstrated dramatic structural changes in nematode cuticle treated with the purified protease. A partial peptide sequence obtained by N-terminal sequence analysis was used to design degenerate primers for the isolation of a cDNA gene encoding the mature protease. Analysis of the cDNA and corresponding genomic sequence revealed 97% identity with PII, a gene previously described from A. oligospora, and we conclude that this gene is likely a PII ortholog.