Steady-state kinetics and thermodynamics of the hydrolysis of beta-lactoglobulin by trypsin

Hydrolysis of beta-lactoglobulin (in an equimolar mixture of the A and B variant) by trypsin in neutral aqueous solution [pH 7.7 at 25 degrees C, ionic strength 0.08 (NaCl)] was followed by capillary electrophoresis and thermodynamic parameters derived from a Michaelis-Menten analysis of rate data obtained at 10, 20, 30, and 40 degrees C for disappearance of beta-lactoglobulin. Enthalpy of substrate binding to the enzyme and the energy of activation for the catalytic process were found to have the values, DeltaH(bind) = -28 +/- 4 kJ mol(-)(1) and E(a) = 51 +/- 18 kJ mol(-)(1), respectively. Thus, beta-lactoglobulin shows an enthalpy of activation for free substrate reacting with free enzyme of about 21 kJ mol(-)(1), corresponding to a transition state stabilization of 60 kJ mol(-)(1) when compared to acid-catalyzed hydrolysis. The catalytic efficiency of trypsin in hydrolysis of beta-lactoglobulin is increased significantly by temperature; however, this effect is partly counteracted by a weaker substrate binding resulting in an increase by only 25%/10 degrees C in overall catalytic efficiency.

Standardized reaction times used to describe the mechanism of enzyme-induced gelation in whey protein systems

Whey protein isolate (WPI), either untreated or pretreated at 80 degrees C for 30 min, was incubated with a proteinase from Bacillus licheniformis until a gel was formed. Standardized reaction times, directly linked to the degree of hydrolysis, were obtained from plots of the relative amount of peptides released v. reaction time obtained under different conditions (enzyme concentration, temperature, pH, NaCl addition). This provided a connection between the gelation profile and the degree of hydrolysis. In the case of untreated WPI, gelation occurred at lower degrees of proteolysis when the enzyme concentration was decreased, demonstrating that a rate-limiting aggregation process occurred at the same time as the proteolysis in a manner similar to the renneting of milk. This was not the case for preheated WPI, when gelation was found to take place at a constant degree of proteolysis, independent of the enzyme concentration. In this case, the mechanism could be described by assuming the thermally induced aggregates present in this substrate had progressively more stabilizing peptide segments shaved off, resulting in increased attraction between individual aggregates that ultimately led to gelation. Results obtained at 40-60 degrees C supported this, as we found no effect of temperature on the degree of proteolysis at gelation for the untreated WPI, whereas the degree of proteolysis decreased with increasing temperature when heated WPI was hydrolysed. The effect of pH and NaCl addition on the process was to reduce repulsion between the aggregating species so that gelation was induced at a decreased degree of proteolysis.

Identification of peptides in aggregates formed during hydrolysis of beta-lactoglobulin B with a Glu and Asp specific microbial protease

The purpose of the present study was to identify the peptides responsible for aggregate formation during hydrolysis of beta-lactoglobulin by BLP at neutral pH. Hydrolysates taken at various stages of aggregate formation were separated into a precipitate and a soluble phase and each was analyzed by CE and mass spectrometry. The aggregates consisted of six to seven major peptides of which four were tentatively identified. The peptides were positively charged at neutral pH and had a high charge-to-mass ratio at low pH. The fragment f135-158 seemed to be the initiator of aggregation, since it was present at high concentration in the aggregates at all stages, and the concentration of this peptide remained low in the supernatant. F135-158 contains several basic and acid amino acids alternating with hydrophobic amino acids, which is in accordance with formation of noncovalently linked aggregates, as previously shown.

Association of JC virus large T antigen with myelin basic protein transcription factor (MEF-1/Puralpha) in hypomyelinated brains of mice transgenically expressing T antigen

Progressive multifocal leukoencephalopathy (PML) is a fatal demyelinating disease caused by cytolytic destruction of oligodendrocytes, the myelin-producing cells of the central nervous system, by the human neurotropic JC virus (JCV). The early protein of JCV, T antigen, which is produced at the early stage of infection, is important for orchestrating the events leading to viral lytic infection and cytolytic destruction of oligodendrocytes. Results from transgenic mouse studies, however, have revealed that, in the absence of lytic infection, this protein can induce brain hypomyelination and suppression of myelin gene expression. Since expression of the gene encoding myelin basic protein, the major component of myelin, can be regulated by a DNA-binding transcription factor, MEF-1/Puralpha, (Puralpha), we have examined the level of this protein in transgenic mouse brains. Results from immunoprecipitation and Western blots showed that while there was no drastic decrease in the level of MEF-1/Puralpha in transgenic mouse brains, JCV T antigen was found in a complex with MEF-1/Puralpha. Immunohistological studies revealed abnormal oligodendrocytes in white matter, where MEF-1/Puralpha and T antigen were detected. Furthermore, immunogold electron microscopic studies revealed that Puralpha and T antigen are colocalized in the nucleus of the oligodendrocytes and in hippocampal neurons. Interestingly, results from cell culture studies revealed that incubation of oligodendrocytes with JCV led to a drastic decrease in the level of MEF-1/Puralpha protein. These observations provide insight into the molecular pathogenesis of PML and support a model for a dual effect of JCV on inducing hypomyelination by (i) affecting myelin gene expression via interaction of JCV T antigen and the myelin gene transcription factor, MEF-1/Puralpha, and (ii) causing a decline in the level of the host regulatory proteins, including MEF-1/Puralpha, which are involved in myelin gene expression.

Human ubiquitous JCV(CY) T-antigen gene induces brain tumors in experimental animals

JCV is a papovavirus which is widespread in the human population. The prototype Mad-1 variant of JCV induces a fatal demyelinating disease of the central nervous system (CNS) called Progressive Multifocal Leukoencephalopathy (PML) in immunosuppressed individuals. The unique tropism of JCV (Mad-1) to the CNS is attributed to the tissue-specific regulation of the viral early promoter which is responsible for the production of the viral regulatory protein, T-antigen. The archetype form of this virus, JCV(CY), which has been repeatedly isolated from the urine of PML and non-PML individuals, is distinct from JCV(Mad-1) in the structural organization of the regulatory sequence. To characterize the tissue specific expression of JCV(CY) and to investigate its potential in inducing disease, transgenic mice containing the early region of JCV(CY) were generated. Some of these mice between 9-13 months of age exhibited signs of illness as manifested by paralysis of rear limbs, hunched posture, and poor grooming. Neuropathological examination indicated no sign of hypomyelination of the brain, but surprisingly, revealed the presence of primitive tumors originating from the cerebellum and the surrounding brain stem. The tumor masses also infiltrated the surrounding tissue. Results from RNA and protein studies revealed a high level of T-antigen mRNA expression in hindbrains of clinically normal and affected transgenic mice. However, higher levels of T-antigen RNA and protein were detected in brains of the animals exhibiting severe illness. The close resemblance of JCV(CY) induced tumor in transgenic mice to the human medulloblastoma/primitive neuroectodermal tumor (PNETs) in location, histologic appearance, and expression of marker proteins strongly suggests the utility of this novel animal model for the study of human brain tumors.

Oncogenic potential of human neurotropic papovavirus, JCV, in CNS

The human polyomavirus, JCV, is the causative agent of Progressive Multifocal Leukoencephalopathy (PML), a fatal human demyelinating disease. PML results from the cytolytic destruction of oligodendrocytes, the myelin-producing cells of the nervous system. JCV has also been shown to be tumorigenic in several animal models. Transgenic mice expressing the JCV early protein, T-antigen, develop poorly differentiated neural crest origin tumours. Intracerebral inoculation of JCV into newborn hamsters induces medulloblastomas, astrocytomas, and primitive neuroectodermal tumours. Further, inoculation of the virus into the brains of non-human primates, owl and squirrel monkeys, results in astrocytomas and glioblastoma multiforme. Several case reports have associated JCV with human CNS tumours in patients with concomitant PML, and one such report has detected JCV in a glial tumour in the absence of PML. The induction of neural origin tumours by JCV has been studied in transgenic mice harbouring the early genome of the virus. Alterations in the level and function of tumour suppressor proteins p53 and Rb, as well as associated cell cycle regulators, have been detected in tumour tissue from JCV T-antigen transgenic mice. Possible mechanisms by which JCV may exert its oncogenic potential by alteration of cellular growth control pathways in both humans and experimental animals are discussed.

Selective disruption of genes transiently induced in differentiating mouse embryonic stem cells by using gene trap mutagenesis and site-specific recombination

A strategy employing gene trap mutagenesis and site-specific recombination (Cre/loxP) has been used to identify genes that are transiently expressed during early mouse development. Embryonic stem cells expressing a reporter plasmid that codes for neomycin phosphotransferase and Escherichia coli LacZ were infected with a retroviral gene trap vector (U3Cre) carrying coding sequences for Cre recombinase (Cre) in the U3 region. Activation of Cre expression from integrations into active genes resulted in a permanent switching between the two selectable marker genes and consequently the expression of beta-galactosidase (beta-Gal). As a result, clones in which U3Cre had disrupted genes that were only transiently expressed could be selected. Moreover, U3Cre-activating cells acquired a cell autonomous marker that could be traced to cells and tissues of the developing embryo. Thus, when two of the clones with inducible U3Cre integrations were passaged in the germ line, they generated spatial patterns of beta-Gal expression.

Effect of different East Coast Fever control strategies on fertility, milk production and weight gain of Sanga cattle in the Central Province of Zambia

Five different East Coast Fever (ECF) (Theileria parva infection) control strategies, based on tick control and/or ECF immunization, were tested in groups of traditionally managed Sanga cattle in the Central Province of Zambia over a period of 2.5 years. Two groups were kept under intensive tick control (sprayed weekly), one group immunized and one non-immunized. Two further groups were under no tick control, one group immunized and one non-immunized, while a fifth group was immunized against ECF and maintained under strategic tick control (18 sprays per year). Tick control increased milk production and weight gain but not fertility. Immunization had neither marked detrimental nor beneficial effects on the cattle productivity. The combination of strategic tick control and immunization resulted in the highest level of production and at the same time reduced the potential risk from other tick-borne diseases.

Role of cell cycle regulators in tumor formation in transgenic mice expressing the human neurotropic virus, JCV, early protein

Transgenic mice harboring the early genome from the human neurotropic JC virus, JCV, develop massive abdominal tumors of neural crest origin during 6-8 months after birth and succumb to death a few weeks later. The viral early protein, T-antigen, which possesses the ability to transform cells of neural origin, is highly expressed in the tumor cells. Immunoblot analysis of protein extract from tumor tissue shows high level expression of the tumor suppressor protein, p53, in complex with T-antigen. Expression of p21, a downstream target for p53, which controls cell cycle progression by regulating the activity of cyclins and their associated kinases during the G1 phase, is extremely low in the tumor cells. Whereas the level of expression and activity of cyclin D1 and its associated kinase, cdk6, was modest in tumor cells, both cyclin A and E, and their kinase partners, cdk2 and cdk4, were highly expressed and exhibited significant kinase activity. The retinoblastoma gene product, pRb, which upon phosphorylation by cyclins:cdk induces rapid cell proliferation, was found in the phosphorylated state in tumor cell extracts, and was detected in association with JCV T-antigen. The transcription factor, E2F-1, which dissociates from the pRb-E2F-1 complex and stimulates S phase-specific genes upon phosphorylation of pRb and/or complexation of pRb with the viral transforming protein, was highly expressed in tumor cells. Accordingly, high level expression of the E2F-1-responsive gene, proliferating cell nuclear antigen (PCNA), was detected in the tumor cells. These observations suggest a potential regulating pathway that, upon expression of JCV T-antigen, induces formation and progression of tumors of neural origin in a whole animal system.

Molecular characterization of human zyxin

Zyxin is a component of adhesion plaques that has been suggested to perform regulatory functions at these specialized regions of the plasma membrane. Here we describe the isolation and characterization of cDNAs encoding human and mouse zyxin. Both the human and mouse zyxin proteins display a collection of proline-rich sequences as well as three copies of the LIM domain, a zinc finger domain found in many signaling molecules. The human zyxin protein is closely related in sequence to proteins implicated in benign tumorigenesis and steroid receptor binding. Antibodies raised against human zyxin recognize an 84-kDa protein by Western immunoblot analysis. The protein is localized at focal contacts in adherent erythroleukemia cells. By Northern analysis, we show that zyxin is widely expressed in human tissues. The zyxin gene maps to human chromosome 7q32-q36.

Detection of JC virus DNA sequence and expression of the viral oncoprotein, tumor antigen, in brain of immunocompetent patient with oligoastrocytoma

We describe molecular and clinical findings in an immunocompetent patient with an oligoastrocytoma and the concomitant presence of the human papovavirus, JC virus (JCV), which is the etiologic agent of the subacute, debilitating demyelinating disease, progressive multifocal leukoencephalopathy. Histologic review revealed a glial neoplasm consisting primarily of a moderately cellular oligodendroglioma with distinct areas of a fibrillary astrocytoma. Immunohistochemical analysis revealed nuclear staining of tumor cells with antibodies against the viral oncoprotein [tumor antigen (T antigen)], the proliferation marker (Ki67), and the cellular proliferation regulator (p53). Using primers specific to the JCV control region, PCR yielded amplified DNA that was identical to the control region of the Mad-4 strain of the virus. PCR analysis demonstrated the presence of the genome for the viral oncoprotein, T antigen, and results from primer extension studies revealed synthesis of the viral early RNA for T antigen in the tumor tissues. The presence of viral T antigen in the tumor tissue was further demonstrated by immunoblot assay. To our knowledge, this is the first report of the presence of JCV DNA, RNA, and T antigen in tissue in which viral T antigen is localized to tumor cell nuclei and suggests the possible association of JCV with some glial neoplasms.

Evidence that the soluble factors secreted by activated immune cells suppress replication of human neurotropic JC virus DNA in glial cells

Coordination of the immune response to viral infection and disease in the brain is believed to involve bidirectional interaction between the immune system and the central nervous system (CNS). Progressive multifocal leukoencephalopathy (PML) is a demyelinating disease of the CNS that generally affects patients exhibiting an immunocompromised condition due to various illnesses. The human polyomavirus, JCV, which infects greater than 70% of the adult population is the etiological agent of this disease. Infection with JCV occurs during childhood and the virus remains in the latent state with no apparent clinical signals. However, under immunocompromised conditions, the virus enters the lytic cycle, and upon cytolytic destruction of glial cells, causes PML. To understand the molecular mechanism underlying immune regulation of JCV replication, we have developed a cell culture system and have investigated the effect of soluble factors from T-cell cultures on replication of JCV DNA in glial cells. Our data demonstrate that replication of JCV DNA in the presence of PMA-stimulated T-cell supernatant is substantially decreased in transfected glial cells. Heat-inactivation and size-fractionation studies revealed participation of a heat labile factor(s) which loses its maximum activity at 60 degrees and ranges between 30 and 100 kDa in size. The unfractionated T-cell supernatant and the fraction enriched in 30- to 100-kDa proteins reduced the level of viral DNA replication during the early phase of the lytic cycle. These observations suggest that regulatory factors which are secreted by immune cells may modulate the level of JCV DNA replication in glial cells. The importance of these observations in reactivation of JCV in immunocompromised individuals and development of PML is discussed.

Differential regulation of plasminogen activator and inhibitor gene transcription by the tumor suppressor p53

The ability of p53 to activate or repress transcription suggests that its biological function as tumor suppressor is in part accomplished by regulating a number of genes including such required for inhibition of cell growth. We here give evidence that p53 also may regulate genes responsible for the proteolytic degradation of the extracellular matrix, which is considered a crucial feature for local invasion and metastasis of neoplastic cells. An important and highly regulated cascade of such proteolytic events involves the plasminogen activator system. We show that wild-type p53 represses transcription from the enhancer and promoter of the human urokinase-type (u-PA) and the tissue-type plasminogen activator (t-PA) gene through a non-DNA binding mechanism. Oncogenic mutants lost the repressing activity. In contrast, wild-type but not mutant p53 specifically binds to and activates the promoter of the plasminogen activator inhibitor type-1 (PAI-1) gene. Interestingly, one of the p53 mutants (273his) inhibited PAI-1 promoter activity. Our results suggest that altered function of oncogenic forms of p53 may lead to altered expression of the plasminogen activators and their inhibitor(s) and thus to altered activation of the plasminogen/plasmin system during tumor progression.

Micellar electrokinetic capillary chromatography for determination of indolyl glucosinolates and transformation products thereof

Micellar electrokinetic capillary chromatography based on dodecyltrimethylammonium bromide as a surfactant has been developed for the qualitative and quantitative determination of indolylic compounds. Indolyl glucosinolates (indol-3-ylmethylglucosinolates), its degradation products, and further transformation products thereof have been included in the studies. The influence of various parameters on the separation has been investigated, resulting in efficient separation, even for structurally closely related compounds, with theoretical plate number per meter of capillary of up to 370,000 for some compounds. Repeatability and linearity of the method have been determined giving relative standard deviations for the migration times of the compounds between 0.5 and 0.9% and linear correlation coefficients between 0.9924 and 0.9996, respectively. The method can be successfully applied to follow the degradation of indolyl glucosinolates in detail.