Rhythmic auditory cueing in atypical parkinsonism: A pilot study

Rhythmic auditory cueing (RAC) can improve gait parameters in neurological disorders such as Parkinson's disease and stroke. However, there is a lack of research on the effects of RAC in patients with atypical parkinsonian disorders (APD). Using a smartphone metronome application, we aimed to investigate the immediate effects of RAC in patients with clinically diagnosed APD, namely Progressive Supranuclear Palsy (PSP-Richardson Syndrome and other variants, PSP-nonRS), Corticobasal Syndrome (CBS), Multiple System Atrophy (MSA), and Dementia with Lewy Bodies (DLB). A total of 46 APD participants (25 PSP, 9 CBS, 8 MSA and 4 DLB; age: mean = 70.17, standard deviation = 7.15) walked at their preferred pace for 2 min without any rhythmic auditory cueing (RAC). Participants then walked the same path for another 2 min with RAC set at a tempo 10% faster than the baseline cadence of each participant. After a 10–15-min break, participants walked the same path for another 2 min without RAC to observe for carryover effects. Gait parameters [cadence (steps/minute), gait velocity (meters/minute), and stride length (centimeters)] were collected at baseline, during RAC, and post-RAC. There was a significant improvement in cadence in all participants from baseline to during RAC and post-RAC (corrected p-values = 0.009 for both). Gait velocity also improved from baseline to during RAC and post-RAC in all participants, although this improvement was not significant after correcting for multiple comparisons. The changes in cadence and gait velocity were most pronounced in PSP. In addition, our exploratory analysis showed that the cadence in the suspected TAU group (PSP+CBS) showed a significant improvement from baseline to during RAC and post-RAC (corr. p-value = 0.004 for both). This pilot study using short-term RAC in APD patients demonstrated improvements in cadence and velocity. There is an urgent need for effective gait rehabilitation modalities for patients with APD, and rhythmic cueing can be a practical and useful intervention to improve their gait pattern.

Wearable sensors detect impaired gait and coordination in LBSL during remote assessments

Background

Leukoencephalopathy with brainstem and spinal cord involvement and lactate elevation (LBSL) is a rare leukodystrophy with motor impairment due to biallelic mutations in DARS2, which encodes mitochondrial aspartyl tRNA synthetase. Progressive ataxia is the primary feature.

Objective

The study objective is to determine the feasibility of remotely collecting quantitative gait and balance measures in LBSL.

Methods

The study design uses wearable accelerometers and the scale for the assessment and rating of ataxia (SARA) scale to assess gait and postural sway in LBSL and control participants' homes through video conferencing.

Results

Lateral step variability (LSV), which indicates stride variability, and elevation of the step at mid‐swing are increased for LBSL patients during brief walking tests. During stance with the eyes closed, LBSL participants show rapid accelerations and decelerations of body movement covering a large sway area and path. Both the LSV and sway area during stance with the feet together and eyes closed correlate strongly with the SARA.

Conclusions

Wearable accelerometers are valid and sensitive for detecting ataxia in LBSL patients during remote assessments. The finding of large increases in the sway area during stance with the eyes closed is intriguing since dorsal column dysfunction is universally seen in LBSL. This approach can be applied to related rare diseases that feature ataxia.

Does case-based blended-learning expedite the transfer of declarative knowledge to procedural knowledge in practice?

BACKGROUND

Case-Based Learning (CBL) has seen widespread implementation in undergraduate education since the early 1920s. Ample data has shown CBL to be an enjoyable and motivational didactic tool, and effective in assisting the expansion of declarative and procedural knowledge in academia. Although a plethora of studies apply multiple choice questions (MCQs) in their investigation, few studies measure CBL or case-based blended learning (CBBL)-mediated changes in students' procedural knowledge in practice or employ comparison or control groups in isolating causal relationships.

METHODS

Utilizing the flexibilities of an e-learning platform, a CBBL framework consisting of a) anonymized patient cases, b) case-related textbook material and online e-CBL modules, and c) simulated patient (SP) contact seminars, was developed and implemented in multiple medical fields for undergraduate medical education. Additionally, other fields saw a solo implementation of e-CBL in the same format. E- cases were constructed according to the criteria of Bloom's taxonomy. In this study, Objective Structured Clinical Examination (OSCE) results from 1886 medical students were analyzed in total, stratified into the following groups: medical students in 2013 (n = 619) before CBBL implementation, and after CBBL implementation in 2015 (n = 624) and 2016 (n = 643).

RESULTS

A significant improvement (adjusted p = .002) of the mean OSCE score by 1.02 points was seen between 2013 and 2015 (min = 0, max = 25).

CONCLUSION

E-Case-Based Learning is an effective tool in improving performance outcomes and may provide a sustainable learning platform for many fields of medicine in future.

The search for attitude-a hidden curriculum assessment from a central European perspective

BACKGROUND

Little is known about the development of the hidden curriculum in the medical education system. It refers to a conglomeration of implicit beliefs, attitudes and forms of conduct that are unwittingly transmitted from one generation of teaching physicians to the next. How can we describe this process, what are the potential positive or negative impacts, and last but not least, how can we measure it?

METHODS

Students of the Medical University of Vienna complete their clinical rotations in Vienna and in other accredited, mostly central European hospitals. They were subsequently invited to evaluate their rotations in an online questionnaire regarding dimensions, such as professionalism, teaching, integration and appreciation.

RESULTS

In total, 133 students participated in this pilot study and the average response rate was 10.1%, similar to evaluations conducted prior to that. Although the evaluation results on average were positive, several experiences of deprecation and less professional conduct were present in each evaluated rotation. Giving the students the opportunity to reflect upon their experiences could be seen as an intervention and investigation at the same time.

CONCLUSIONS

This survey serves as a precursor to a qualitative interview-based study, accompanying the implementation of case-based learning designed by collaborating residents and medical students. The findings of this pilot-study support the necessity of fostering a reflective capacity in the education of medical students, enabling them to speak up and live up to the expected professionalism despite shortcomings within the hidden curriculum.

Siramesine triggers cell death through destabilisation of mitochondria, but not lysosomes

A sigma-2 receptor agonist siramesine has been shown to trigger cell death of cancer cells and to exhibit a potent anticancer activity in vivo. However, its mechanism of action is still poorly understood. We show that siramesine can induce rapid cell death in a number of cell lines at concentrations above 20 μM. In HaCaT cells, cell death was accompanied by caspase activation, rapid loss of mitochondrial membrane potential (MMP), cytochrome c release, cardiolipin peroxidation and typical apoptotic morphology, whereas in U-87MG cells most apoptotic hallmarks were not notable, although MMP was rapidly lost. In contrast to the rapid loss of MMP above 20 μM siramesine, a rapid increase in lysosomal pH was observed at all concentrations tested (5–40 μM); however, it was not accompanied by lysosomal membrane permeabilisation (LMP) and the release of lysosomal enzymes into the cytosol. Increased lysosomal pH reduced the lysosomal degradation potential as indicated by the accumulation of immature forms of cysteine cathepsins. The lipophilic antioxidant α-tocopherol, but not the hydrophilic antioxidant N-acetyl-cysteine, considerably reduced cell death and destabilisation of mitochondrial membranes, but did not prevent the increase in lysosomal pH. At concentrations below 15 μM, siramesine triggered cell death after 2 days or later, which seems to be associated with a general metabolic and energy imbalance due to defects in the endocytic pathway, intracellular trafficking and energy production, and not by a specific molecular event. Overall, we show that cell death in siramesine-treated cells is induced by destabilisation of mitochondria and is independent of LMP and the release of cathepsins into the cytosol. Moreover, it is unlikely that siramesine acts exclusively through sigma-2 receptors, but rather through multiple molecular targets inside the cell. Our findings are therefore of significant importance in designing the next generation of siramesine analogues with high anticancer potential.

MAGUKs, scaffolding proteins at cell junctions, are substrates of different proteases during apoptosis

A major feature of apoptotic cell death is gross structural changes, one of which is the loss of cell–cell contacts. The caspases, executioners of apoptosis, were shown to cleave several proteins involved in the formation of cell junctions. The membrane-associated guanylate kinases (MAGUKs), which are typically associated with cell junctions, have a major role in the organization of protein–protein complexes at plasma membranes and are therefore potentially important caspase targets during apoptosis. We report here that MAGUKs are cleaved and/or degraded by executioner caspases, granzyme B and several cysteine cathepsins in vitro. When apoptosis was induced by UV-irradiation and staurosporine in different epithelial cell lines, caspases were found to efficiently cleave MAGUKs in these cell models, as the cleavages could be prevented by a pan-caspase inhibitor N-benzyloxycarbonyl-Val-Ala-Asp(OMe)fluoromethylketone. Using a selective lysosomal disrupting agent -leucyl--leucine methyl ester, which induces apoptosis through the lysosomal pathway, it was further shown that MAGUKs are also cleaved by the cathepsins in HaCaT and CaCo-2 cells. Immunohistological data showed rapid loss of MAGUKs at the sites of cell–cell contacts, preceding actual cell detachment, suggesting that cleavage of MAGUKs is an important step in fast and efficient cell detachment.

Reduced tumour cell proliferation and delayed development of high-grade mammary carcinomas in cathepsin B-deficient mice

Expression levels of the papain-like cysteine protease cathepsin B (Ctsb) have been positively correlated with mammary tumour progression and metastasis; however, its roles in the hallmark processes of malignant growth remain poorly defined. Using Ctsb-deficient mice we investigated tumour cell differentiation, proliferation and apoptosis in the Tg(MMTV-PyMT) mouse mammary cancer model. Absence of Ctsb significantly impaired development of high-grade invasive ductal carcinomas and reduced the metastatic burden in the lungs. Mice lacking Ctsb exhibited reduced cell proliferation in mammary carcinomas and their lung metastases. Notably, intravenous injection of primarily isolated, Ctsb-expressing tumour cells into congenic Ctsb-deficient mice revealed impaired cell proliferation in the resulting experimental lung metastases, providing evidence for the involvement of Ctsb in paracrine regulation of cancer cell proliferation. No Ctsb genotype-dependent difference in tumour cell death was observed in vivo or by treatment of isolated PyMT cancer cells with tumour necrosis factor-alpha. However, cancer cells lacking Ctsb exhibited significantly higher resistance to apoptosis induction by the lysosomotropic agent Leu-Leu-OMe. Thus, our results indicate an in vivo role for Ctsb in promoting cellular anaplasia in mammary cancers and proliferation in lung metastases.

Cysteine cathepsins in the immune response

Antigen (Ag) processing by major histocompatibility complex class II (MHC) class II molecules is tightly linked with the proteases of the endosomal/lysosomal system. Cysteine (Cys) cathepsins, which constitute a major portion of this proteolytic system, have been found to have essential roles in both Ag processing and maturation of the MHC class II molecules. In this review, we will cover some specific functions of individual Cys cathepsins and particularly those most relevant to the immune system.

Apoptosis caused by cathepsins does not require Bid signaling in an in vivo model of progressive myoclonus epilepsy (EPM1)

Apoptosis can be mediated by mechanisms other than the traditional caspase-mediated cleavage cascade. There is growing recognition that alternative proteolytic enzymes such as the lysosomal cathepsin proteases can initiate or propagate proapoptotic signals, but it is currently unclear how cathepsins achieve these actions. Recent in vitro evidence suggests that cathepsins cleave the proapoptotic Bcl-2 family member Bid, thereby activating it and allowing it to induce the mitochondrial release of cytochrome c and subsequent apoptosis. We have tested this hypothesis in vivo by breeding mice that lack cathepsin inhibition (cystatin B-deficient mice) to Bid-deficient mice, to determine whether the apoptosis caused by cathepsins is dependent on Bid signaling. We found that cathepsins are still able to promote apoptosis even in the absence of Bid, indicating that these proteases mediate apoptosis via a different pathway, or that some other molecule can functionally substitute for Bid in this system.

Inhibition of papain-like cysteine proteases and legumain by caspase-specific inhibitors: when reaction mechanism is more important than specificity

We report here that a number of commonly used small peptide caspase inhibitors consisting of a caspase recognition sequence linked to chloromethylketone, fluoromethylketone or aldehyde reactive group efficiently inhibit other cysteine proteases than caspases. The in vitro studies included cathepsins B, H, L, S, K, F, V, X and C, papain and legumain. Z-DEVD-cmk was shown to be the preferred irreversible inhibitor of most of the cathepsins in vitro, followed by Z-DEVD-fmk, Ac-YVAD-cmk, Z-YVAD-fmk and Z-VAD-fmk. Inactivation of legumain by all the inhibitors investigated was moderate, whereas cathepsins H and C were poorly inhibited or not inhibited at all. Inhibition by aldehydes was not very potent. All the three fluoromethylketones efficiently inhibited cathepsins in Jurkat and human embryonic kidney 293 cells at concentrations of 100 microM. Furthermore, they completely inhibited cathepsins B and X activity in tissue extracts at concentrations as low as 1 microM. These results suggest that data based on the use of these inhibitors should be taken with caution and that other proteases may be implicated in the processes previously ascribed solely to caspases.

Surgical options in colorectal injuries

Colonic or rectal injuries occur in up to 10% of patients that suffer penetrating or severe blunt abdominal trauma. The majority of colon injuries are diagnosed intraoperatively following a penetrating abdominal injury. Rectal injuries are usually diagnosed preoperatively with a high index of suspicion based upon the wounding missile trajectory. The vast majority of colon injuries can be primarily repaired with a significant trend toward avoiding colostomy whenever possible. Colostomy is increasingly reserved for rectal injuries and destructive colon injuries with extenuating circumstances such as hemodynamic instability and significant associated injuries.

Abdominal stab wounds: diagnostic peritoneal lavage criteria for emergency room discharge

OBJECTIVE

To prospectively evaluate a method for management of abdominal stab wounds that allows for immediate emergency room discharge.

METHODS

Anterior abdominal stab wound patients were prospectively placed in a study trial during a 48-month period. Consent was obtained for all patients before study entry. Anatomic boundaries for abdominal stab wounds were costal margins, inguinal ligaments, and anterior axillary lines. Hemodynamically stable patients with negative physical examinations were entered in the study and evaluated with closed diagnostic peritoneal lavage (DPL). Patients with DPL results less than 1000 RBCs/mm3 were sent home. Patients with DPL results greater than 1000 RBCs/mm3 (including gross blood) were admitted for observation. Hemodynamically stable patients with evisceration and no abdominal tenderness had the viscera replaced in the emergency room. Eviscerated patients did not undergo DPL and were admitted for observation. Patients that presented with hemodynamic instability or peritonitis were not entered in the study and underwent immediate surgical intervention.

RESULTS

Ninety hemodynamically stable patients were entered in the study. Forty-four (49%) patients had DPL < 1000 RBCs/mm3, 34 of which were discharged home. Of the 10 admissions that qualified for discharge, 4 were admitted due to elevated ethanol levels and no family assistance, 3 were admitted to psychiatry, and 3 required other surgical procedures. No patient with DPL < 1000 RBCs/mm3 required laparotomy or had complications associated with their stab wounds. Thirty-eight (42%) patients were observed because DPL counts were greater than 1000 RBCs/mm3. Eight (21%) of these patients developed positive physical examinations that prompted exploratory laparotomy, of which five (63%) were therapeutic. There were no complications associated with delayed laparotomy. Four (4%) patients had DPL results greater than 500 WBCs/mm3, all of which underwent immediate exploratory laparotomy. Four (4%) patients presented with evisceration, one of which underwent therapeutic laparotomy.

CONCLUSION

Abdominal stab wound patients that are hemodynamically stable can be safely sent home from the emergency room when DPL counts are less than 1000 RBCs/mm3. Observation of hemodynamically stable patients allows for low laparotomy rates with minimal morbidity.

Lysosomal cysteine proteases: facts and opportunities

From their discovery in the first half of the 20th century, lysosomal cysteine proteases have come a long way: from being the enzymes non-selectively degrading proteins in lysosomes to being those responsible for a number of important cellular processes. Some of the features and roles of their structures, specificity, regulation and physiology are discussed.

Kinetic study of two novel enantiomeric tricyclic beta-lactams which efficiently inactivate class C beta-lactamases

A detailed kinetic study of the interaction between two ethylidene derivatives of tricyclic carbapenems, Lek 156 and Lek 157, and representative beta-lactamases and D-alanyl-D-alanine peptidases (DD-peptidases) is presented. Both compounds are very efficient inactivators of the Enterobacter cloacae 908R beta-lactamase, which is usually resistant to inhibition. Preliminary experiments indicate that various extended-spectrum class C beta-lactamases (ACT-1, CMY-1, and MIR-1) are also inactivated. With the E. cloacae 908R enzyme, complete inactivation occurs with a second-order rate constant, k(2)/K', of 2 x 10(4) to 4 x 10(4) M(-1) s(-1), and reactivation is very slow, with a half-life of >1 h. Accordingly, Lek 157 significantly decreases the MIC of ampicillin for E. cloacae P99, a constitutive class C beta-lactamase overproducer. With the other serine beta-lactamases tested, the covalent adducts exhibit a wide range of stabilities, with half-lives ranging from long (>4 h with the TEM-1 class A enzyme), to medium (10 to 20 min with the OXA-10 class D enzyme), to short (0.2 to 0.4 s with the NmcA class A beta-lactamase). By contrast, both carbapenems behave as good substrates of the Bacillus cereus metallo-beta-lactamase (class B). The Streptomyces sp. strain R61 and K15 extracellular DD-peptidases exhibit low levels of sensitivity to both compounds.

Human recombinant pro-dipeptidyl peptidase I (cathepsin C) can be activated by cathepsins L and S but not by autocatalytic processing

Human dipeptidyl peptidase I was expressed in the insect cell/baculovirus system and purified in its active (rhDPPI) and precursor (pro-rhDPPI) forms. RhDPPI was very similar to the purified enzyme (hDPPI) with respect to glycosylation, enzymatic processing, oligomeric structure, CD spectra, and catalytic activity. The precursor, which was a dimer, could be activated approximately 2000-fold with papain. Cathepsin L efficiently activated pro-rhDPPI in vitro at pH 4.5 (k(app) approximately 2 x 10(3) min(-)(1) M(-)(1)), and two cleavage pathways were characterized. The initial cleavage was within the pro region between the residual pro part and the activation peptide. Subsequently, the activation peptide was cleaved from the catalytic region, and the latter was cleaved into the heavy and light chains. Alternatively, the pro region was first separated from the catalytic region. Cathepsin S was a less efficient activating enzyme. Cathepsin B and rhDPPI did not activate pro-rhDPPI, and the proenzyme was incapable of autoactivation. Incubation of both pro-rhDPPI and rhDPPI with cathepsin D resulted in degradation. Cystatin C and stefins A and B inhibited rhDPPI with K(i) values in the nanomolar range (K(i) = 0.5-1.1 nM). The results suggest that cathepsin L could be an important activator of DPPI in vivo and that cathepsin D and possibly the cystatins may contribute to DPPI downregulation.

Lysosomal protease pathways to apoptosis. Cleavage of bid, not pro-caspases, is the most likely route

We investigated the mechanism of lysosome-mediated cell death using purified recombinant pro-apoptotic proteins, and cell-free extracts from the human neuronal progenitor cell line NT2. Potential effectors were either isolated lysosomes or purified lysosomal proteases. Purified lysosomal cathepsins B, H, K, L, S, and X or an extract of mouse lysosomes did not directly activate either recombinant caspase zymogens or caspase zymogens present in an NT2 cytosolic extract to any significant extent. In contrast, a cathepsin L-related protease from the protozoan parasite Trypanosoma cruzi, cruzipain, showed a measurable caspase activation rate. This demonstrated that members of the papain family can directly activate caspases but that mammalian lysosomal members of this family may have been negatively selected for caspase activation to prevent inappropriate induction of apoptosis. Given the lack of evidence for a direct role in caspase activation by lysosomal proteases, we hypothesized that an indirect mode of caspase activation may involve the Bcl-2 family member Bid. In support of this, Bid was cleaved in the presence of lysosomal extracts, at a site six residues downstream from that seen for pathways involving capase 8. Incubation of mitochondria with Bid that had been cleaved by lysosomal extracts resulted in cytochrome c release. Thus, cleavage of Bid may represent a mechanism by which proteases that have leaked from the lysosomes can precipitate cytochrome c release and subsequent caspase activation. This is supported by the finding that cytosolic extracts from mice ablated in the bid gene are impaired in the ability to release cytochrome c in response to lysosome extracts. Together these data suggest that Bid represents a sensor that allows cells to initiate apoptosis in response to widespread adventitious proteolysis.

Biochemical characterization of human cathepsin X revealed that the enzyme is an exopeptidase, acting as carboxymonopeptidase or carboxydipeptidase

Cathepsin X, purified to homogeneity from human liver, is a single chain glycoprotein with a molecular mass of approximately 33 kDa and pI 5.1-5.3. Cathepsin X was inhibited by stefin A, cystatin C and chicken cystatin (Ki = 1.7-15.0 nM), but poorly or not at all by stefin B (Ki > 250 nM) and L-kininogen, respectively. The enzyme was also inhibited by two specific synthetic cathepsin B inhibitors, CA-074 and GFG-semicarbazone. Cathepsin X was similar to cathepsin B and found to be a carboxypeptidase with preference for a positively charged Arg in P1 position. Contrary to the preference of cathepsin B, cathepsin X normally acts as a carboxymonopeptidase. However, the preference for Arg in the P1 position is so strong that cathepsin X cleaves substrates with Arg in antepenultimate position, acting also as a carboxydipeptidase. A large hydrophobic residue such as Trp is preferred in the P1' position, although the enzyme cleaved all P1' residues investigated (Trp, Phe, Ala, Arg, Pro). Cathepsin X also cleaved substrates with amide-blocked C-terminal carboxyl group with rates similar to those of the unblocked substrates. In contrast, no endopeptidase activity of cathepsin X could be detected on a series of o-aminobenzoic acid-peptidyl-N-[2,-dinitrophenyl]ethylenediamine substrates. Furthermore, the standard cysteine protease methylcoumarine amide substrates (kcat/Km approximately 5.0 x 103 M-1.s-1) were degraded approximately 25-fold less efficiently than the carboxypeptidase substrates (kcat/Km approximately 120.0 x 103 M-1.s-1).

The region of antithrombin interacting with full-length heparin chains outside the high-affinity pentasaccharide sequence extends to Lys136 but not to Lys139

The interaction of a well-defined pentasaccharide sequence of heparin with a specific binding site on antithrombin activates the inhibitor through a conformational change. This change increases the rate of antithrombin inhibition of factor Xa, whereas acceleration of thrombin inhibition requires binding of both inhibitor and proteinase to the same heparin chain. An extended heparin binding site of antithrombin outside the specific pentasaccharide site has been proposed to account for the higher affinity of the inhibitor for full-length heparin chains by interacting with saccharides adjacent to the pentasaccharide sequence. To resolve conflicting evidence regarding the roles of Lys136 and Lys139 in this extended site, we have mutated the two residues to Ala or Gln. Mutation of Lys136 decreased the antithrombin affinity for full-length heparin by at least 5-fold but minimally altered the affinity for the pentasaccharide. As a result, the full-length heparin and pentasaccharide affinities were comparable. The reduced affinity for full-length heparin was associated with the loss of one ionic interaction and was caused by both a lower overall association rate constant and a higher overall dissociation rate constant. In contrast, mutation of Lys139 affected neither full-length heparin nor pentasaccharide affinity. The rate constants for inhibition of thrombin and factor Xa by the complexes between antithrombin and full-length heparin or pentasaccharide were unaffected by both mutations, indicating that neither Lys136 nor Lys139 is involved in heparin activation of the inhibitor. Together, these results show that Lys136 forms part of the extended heparin binding site of antithrombin that participates in the binding of full-length heparin chains, whereas Lys139 is located outside this site.

Crystal structure of cathepsin X: a flip-flop of the ring of His23 allows carboxy-monopeptidase and carboxy-dipeptidase activity of the protease

BACKGROUND

Cathepsin X is a widespread, abundantly expressed papain-like mammalian lysosomal cysteine protease. It exhibits carboxy-monopeptidase as well as carboxy-dipeptidase activity and shares a similar activity profile with cathepsin B. The latter has been implicated in normal physiological events as well as in various pathological states such as rheumatoid arthritis, Alzheimer's disease and cancer progression. Thus the question is raised as to which of the two enzyme activities has actually been monitored.

RESULTS

The crystal structure of human cathepsin X has been determined at 2.67 A resolution. The structure shares the common features of a papain-like enzyme fold, but with a unique active site. The most pronounced feature of the cathepsin X structure is the mini-loop that includes a short three-residue insertion protruding into the active site of the protease. The residue Tyr27 on one side of the loop forms the surface of the S1 substrate-binding site, and His23 on the other side modulates both carboxy-monopeptidase as well as carboxy-dipeptidase activity of the enzyme by binding the C-terminal carboxyl group of a substrate in two different sidechain conformations.

CONCLUSIONS

The structure of cathepsin X exhibits a binding surface that will assist in the design of specific inhibitors of cathepsin X as well as of cathepsin B and thereby help to clarify the physiological roles of both proteases.

Lysosomal cysteine proteases: more than scavengers

Lysosomal cysteine proteases were believed to be mainly involved in intracellular protein degradation. Under special conditions they have been found outside lysosomes resulting in pathological conditions. With the discovery of a series of new cathepsins with restricted tissue distributions, it has become evident that these enzymes must be involved in a range of specific cellular tasks much broader than as simple housekeeping enzymes. It is therefore timely to review and discuss the various physiological roles of mammalian lysosomal papain-like cysteine proteases as well as their mechanisms of action and the regulation of their activity.

The high stability of cruzipain against pH-induced inactivation is not dependent on its C-terminal domain

Unlike mammalian lysosomal cysteine proteases, the trypanosomal cysteine protease cruzipain contains a 130-amino acid residue C-terminal domain, in addition to the catalytic domain, and it is stable at neutral pH. The endogenous (with C-terminal domain) and recombinant (without C-terminal domain) cruzipains exhibit similar stabilities at both acid (k(inac)=3.1x10(-3) s(-1) and 4.4x10(-3) s(-1) at pH 2.75 for endogenous and recombinant cruzipain, respectively) and alkaline pH (k(inac)=3.0x10(-3) s(-1) and 3. 7x10(-3) s(-1) at pH 9.15 for endogenous and recombinant cruzipain, respectively). The pH-induced inactivation, which is a highly pH dependent first order process, is irreversible and accompanied by significant changes of secondary and tertiary structure as revealed by circular dichroism measurements. The different stability of cruzipain as compared to related proteases, is therefore due mainly to the different number, nature and distribution of charged residues within the catalytic domain and not due to addition of the C-terminal domain.

Autocatalytic processing of recombinant human procathepsin B is a bimolecular process

Cathepsin B and other lysosomal cysteine proteinases are synthesized as inactive zymogens, which are converted to their mature forms by other proteases or by autocatalytic processing. Procathepsin B autoactivation was shown in vitro at pH 4.5 to be a bimolecular process with K(s) and k(cat) values of 2.1+/-0.9 microM and 0.12+/-0.02 s(-1)6.0. However, in the presence of 0.5 microg/ml of dextran sulfate, relatively rapid processing is observed even at pH 6.5 (t(1/2) approximately 90 min), suggesting that glycosaminoglycans are involved in in vivo processing of lysosomal cysteine proteases.

Interaction of cystatin C variants with papain and human cathepsins B, H and L

Recombinant human cystatin C and two of its mutants were expressed in Escherichia coli. The recombinant inhibitor was found to be identical to authentic cystatin C as judged by isoelectric focusing (pI 9.2) and kinetics of inhibition of papain and human cathepsins B, H and L. N-terminal truncation of 8 residues resulted in a decrease of isoelectric point (pI 7.8), but the inhibitory properties were similar to those of recombinant cystatin C, suggesting that Leu9 is a critical residue for the inhibition. The mutation of Trp106 to Ser, however, resulted in a decreased affinity of the inhibitor for the enzymes tested, with the largest effect on cathepsin B inhibition (approximately 100-fold increase in Ki).

A pre-steady-state kinetic analysis of substrate binding to human recombinant deoxycytidine kinase: a model for nucleoside kinase action

Deoxycytidine kinase (dCK) is an enzyme with broad substrate specificity which can phosphorylate pyrimidine and purine deoxynucleosides, including important antiviral and cytostatic agents. In this study, stopped-flow experiments were used to monitor intrinsic fluorescence changes induced upon binding of various phosphate donors (ATP, UTP, and the nonhydrolyzable analogue AMP-PNP) and the acceptor dCyd to recombinant dCK. Monophasic kinetics were observed throughout. The nucleotides as well as dCyd bound to the enzyme by a two-step mechanism, involving a rapid initial equilibrium step, followed by a protein conformational change that is responsible for the fluorescence change. The bimolecular association rate constants for nucleotide binding [(4-10) x 10(3) M-1 s-1] were 2-3 orders of magnitude lower than those for dCyd binding [(1.3-1.5 x 10(6) M-1 s-1]. This difference most likely is due predominantly to the large difference in the forward rate constants of the conformational changes (0.04-0.26 s-1 vs 560-710 s-1). Whereas the kinetics of the binding of ATP, UTP, and AMP-PNP to dCK showed some differences, UTP exhibiting the tightest binding, no significant differences were observed for the binding of dCyd to dCK in the presence or absence of phosphate donors. However, the binding of dCyd to dCK in the presence of ATP or UTP was accompanied by a 1.5- or 3-fold higher quenching amplitude as compared with dCyd alone or in the presence of AMP-PNP. We conclude that ATP and UTP induce a conformational change in the enzyme, thereby enabling efficient phosphoryl transfer.

Mutational analysis of two stefin A epitopes

Stefin A, an intracellular inhibitor of cysteine proteinases, is expressed most abundantly in epithelial cells and in cells of lymphatic origin. In order to study its role in normal and pathological conditions we have prepared and characterized monoclonal antibodies against recombinant stefin A. Two high affinity monoclonal antibodies (mAbs) (A22 and C52) were tested for binding to free and papain-complexed stefin A and to a chimeric inhibitor, consisting of 61 amino acid residues of stefin A and 37 carboxy-terminal residues of stefin B. mAb A22 recognized not only free stefin A but also stefin A in complex with papain. The mAbs were further tested for their cross-reactivity against stefin A and B isolated from different mammalian species. On the basis of sequence similarity and tertiary structure of human stefin A we have prepared three mutants - Glu33Lys, Asp61Gly and Asn62Tyr and their reactivity with the mAbs was tested. The binding affinities of mAb A22 for the Asp61Gly and Asn62Tyr mutants were significantly lower, indicating thatthe two amino acids are part of the stefin A epitope recognized by A22. The binding of both mAbs to the mutants Gly4Arg and Gly4Glu was comparable to wild-type stefin A.

Acidic pH as a physiological regulator of human cathepsin L activity

Human cysteine protease cathepsin L was inactivated at acid pH by a first-order process. The inactivation rate decreased with increasing concentrations of a small synthetic substrate, suggesting that substrates stabilize the active conformation. The substrate-independent inactivation rate constant increased with organic solvent content of the buffer, consistent with internal hydrophobic interactions, disrupted by the organic solvent, also stabilizing the enzyme. Circular dichroism showed that the inactivation is accompanied by large structural changes, a decrease in alpha-helix content being especially pronounced. The high activation energy of the reaction at pH 3.0 (200 kJ.mol-1) supported such a major conformational change occurring. The acid inactivation of cathepsin L was irreversible, consistent with the propeptide being needed for proper folding of the enzyme. Aspartic protease cathepsin D was shown to cleave denatured, but not active cathepsin L, suggesting a potential mechanism for in-vivo regulation and turnover of cathepsin L inside lysosomes.

Revised definition of substrate binding sites of papain-like cysteine proteases

A review of kinetic and structural data has enabled us to reconsider the definition of substrate binding sites in papain-like cysteine proteases. Only three substrate binding sites, S2, S1 and S1', involve main as well as side chain contacts between substrate and enzyme residues. Interactions between the enzymes and the substrate P3 and P2' residues are based on side chains (an exception is cathepsin B which is a carboxydipeptidase), so their interaction surface spreads over a relatively wide area. The location and definition of substrate binding sites beyond S3 and S2' is even more questionable.

The oligosaccharide side chain on Asn-135 of alpha-antithrombin, absent in beta-antithrombin, decreases the heparin affinity of the inhibitor by affecting the heparin-induced conformational change

The beta-form of antithrombin, lacking a carbohydrate side chain on Asn-135, is known to bind heparin more tightly than the fully glycosylated alpha-form. The molecular basis for this difference in affinity was elucidated by rapid-kinetic studies of the binding of heparin and the antithrombin-binding heparin pentasaccharide to plasma and recombinant forms of alpha- and beta-antithrombin. The dissociation equilibrium constant for the first step of the two-step mechanism of binding of both heparin and pentasaccharide to alpha-antithrombin was only slightly higher than that for the binding to the beta-form. The oligosaccharide at Asn-135 thus at most moderately interferes with the initial, weak binding of heparin to alpha-antithrombin. In contrast, the rate constant for the conformational change induced by heparin and pentasaccharide in the second binding step was substantially lower for alpha-antithrombin than for beta-antithrombin. Moreover, the rate constant for the reversal of this conformational change was appreciably higher for the alpha-form than for the beta-form. The carbohydrate side chain at Asn-135 thus reduces the heparin affinity of alpha-antithrombin primarily by interfering with the heparin-induced conformational change. These and previous results suggest a model in which the Asn-135 oligosaccharide of alpha-antithrombin is oriented away from the heparin binding site and does not interfere with the first step of heparin binding. This initial binding induces conformational changes involving extension of helix D into the adjacent region containing Asn-135, which are transmitted to the reactive-bond loop. The resulting decreased conformational flexibility of the Asn-135 oligosaccharide and its close vicinity to the heparin binding site destabilize the activated relative to the native conformation. This effect results in a higher energy for inducing the activated conformation in alpha-antithrombin, leading to a decrease in heparin binding affinity.

Equistatin, a new inhibitor of cysteine proteinases from Actinia equina, is structurally related to thyroglobulin type-1 domain

It is well known that the activities of the lysosomal cysteine proteinases are tightly regulated by their endogenous inhibitors, cystatins. Here we report a new inhibitor of cysteine proteinases isolated from sea anemone Actinia equina. The inhibitor, equistatin, is an acidic protein with pI 4.7 and molecular weight of 14,129. It binds tightly and rapidly to cathepsin L (ka = 5.7 x 10(7) M-1 s-1, Ki = 0.051 nM) and papain (ka = 1.2 x 10(7) M-1 s-1, Ki = 0.57 nM). The lower affinity for cathepsin B (Ki = 1.4 nM) was shown to be due mainly to a lower second order association rate constant (ka = 0.04 x 10(6) M-1 s-1). The inhibitor is composed of 128 amino acids forming two repeated domains with 48% identity. Neither of the domains shows any sequence homology to cystatins, but they do show a significant homology to thyroglobulin type-1 domains. A highly conserved consensus sequence motif of Cys-Trp-Cys-Val together with conserved Cys, Pro, and Gly residues is present in major histocompatibility complex class II-associated p41 invariant chain, nidogen, insulin-like growth factor proteins, saxiphilin domain a, pancreatic carcinoma marker proteins (GA733), and chum salmon egg cysteine proteinase inhibitor. In each of the domains of the equistatin, the three residues are similarly conserved, and the sequences Val-Trp-Cys-Val and Cys-Trp-Cys-Val are present in domains a and b, respectively. We suggest that equistatin belongs to a new superfamily of protein inhibitors of cysteine proteinases named thyroglobulin type-1 domain inhibitors. This superfamily currently includes equistatin, major histocompatibility complex class II- associated p41 invariant chain fragment, and chum salmon egg cysteine proteinase inhibitor.

Structural and functional aspects of papain-like cysteine proteinases and their protein inhibitors

Cysteine proteinases are widely distributed among living organisms. According to the most recent classifications (Rawlings and Barrett, 1993, 1994), they can be subdivided on the basis of sequence homology into 14 or even 20 different families, the most important being the papain and the calpain families. The papain-like cysteine proteinases are the most abundant among the cysteine proteinases. The family consists of papain and related plant proteinases such as chymopapain, caricain, bromelain, actinidin, ficin, and aleurain, and the lysosomal cathepsins B, H, L, S, C and K. Most of these enzymes are relatively small proteins with Mr values in the range 20000-35000 (reviewed in Brocklehurst et al., 1987; Polgar, 1989; Rawlings and Barrett, 1994; Berti and Storer, 1995), with the exception of cathepsin C, which is an oligomeric enzyme with Mr approximately 200000 (Metrione et al., 1970; Dolenc et al., 1995). A number of cysteine proteinases are located within lysosomes. Four of them, cathepsins B, C, H and L, are ubiquitous in lysosomes of animals, whereas cathepsin S has a more restricted localisation (Barrett and Kirschke, 1981; Kirschke and Wiederanders, 1994). The enzymes, except cathepsin C, are endopeptidases (reviewed in Kirschke et al., 1995), although cathepsin B was found also to be a dipeptidyl carboxypeptidase (Aronson and Barrett, 1978) and cathepsin H also an aminopeptidase (Koga et al., 1992). Cathepsin C is a dipeptidyl aminopeptidase, but at higher pH it exhibits also dipeptidyl transferase activity (reviewed in Kirschke et al., 1995). Among the lysosomal cysteine proteinases, cathepsin L was found to be the most active in degradation of protein substrates, such as collagen, elastin and azocasein (Barrett and Kirschke, 1981; Maciewicz et al., 1987; Mason et al., 1989), arid cathepsin B the most abundant (Kirschke and Barrett, 1981). All the enzymes are optimally active at slightly acidic pH, although their pH optima for degradation of synthetic substrates vary from 5.5 for cathepsin L to 6.8 for cathepsin H (reviewed in Kirschke et al., 1995). Several other lysosomal cysteine proteinases, such as cathepsins N, T and K, are known, although their properties are less well characterised (reviewed in Kirschke et al., 1995). In particular cathepsin K has attracted recent interest (Bromme et al., 1996; Shi et al., 1995; Bossard et al., 1996; Drake et al., 1996) and was found to be expressed specifically in osteoclasts (Drake et al., 1996) with properties similar to cathepsin L (Bossard et al., 1996).

Crystallographic and fluorescence studies of ligand binding to N-carbamoylsarcosine amidohydrolase from Arthrobacter sp

Crystal structures of N-carbamoylsarcosine amidohydrolase (CSHase; EC 3.5.1.59) have been analyzed by X-ray diffraction methods with two different inhibitors bound to the active site at 2.28 A and 2.37 A resolution. The catalytic center of the enzyme could be identified on the basis of these structures. The four substrate binding sites are situated at the intersubunit interfaces of the compact dimers AB and CD of the homotetrameric enzyme. Both inhibitors inactivate the enzyme irreversibly through covalent binding of their aldehyde groups to the thiol group of the active-site cysteine residue Cys177. Within the identified substrate binding sites a number of residues from different subunits are involved in hydrogen bonding of the inhibitors. Two residues (Ala172 and Thr173) that form an unusual cis-peptide bond at the binding site are important components in fixing the examined inhibitors by hydrogen bonds. An electrochemical enzyme assay for CSHase was used to test the effect of inhibitors and substrate analogs on the enzyme's activity, revealing the high substrate specificity of CSHase. The intrinsic tryptophan fluorescence of CSHase increases strongly upon substrate and inhibitor binding. As most of the tryptophyl residues are located at the active sites, they are thus considerably affected by ligand binding. Fluorescence-detected stopped-flow measurements have been used to study the kinetics of glyoxylate and substrate binding to CSHase. Substrate and inhibitor binding could clearly be distinguished in the stopped-flow experiments. Inhibitor binding reveals at least three different elementary processes, whereas substrate binding is much faster and contains phases with different signs in amplitude.

Interaction of human cathepsin C with chicken cystatin

Cathepsin C was purified from human spleen by a rapid procedure, which included homogenization, ammonium sulfate precipitation, gel filtration on Sephacryl S-200 and finally affinity chromatography on chicken cystatin-Sepharose. The interaction between cathepsin C and chicken cystatin was further characterized. It was found to be accompanied by a maximum decrease in fluorescence emission intensity at 336 nm. Fluorescence titration showed that human cathepsin C can bind four chicken cystatin molecules. The 4:1 binding stoichiometry was confirmed by titration monitored by the loss of enzyme activity. A non-competitive-competitive type of inhibition was determined from a double-reciprocal Lineweaver-Burk plot with a Ki value of 0.22 nM for the non-competitive inhibition.

High-molecular-weight kininogen binds two molecules of cysteine proteinases with different rate constants

Fluorescence titrations showed that high-molecular-weight kininogen binds two molecules of papain, cruzipain and cathepsin S with high affinity. The 2:1 binding stoichiometry was confirmed by stopped-flow kinetic measurements of papain binding, which also revealed that the two sites bind the enzyme with different association rate constants (kass,1 = 23.0 x 10(6) M-1 s-1 and kass,2 = 3.4 x 10(6) M-1 s-1). As for low-molecular-weight kininogen, comparison of these kinetic constants with previous data for intact low- and high-molecular-weight kininogen and the separated domains indicated that the faster-binding site is also the tighter-binding site and is that of domain 3, whereas the slower-binding, lower-affinity site is on domain 2. The results further demonstrate that there is no appreciable steric interference between the two domains or by the kininogen light chain in the binding of proteinases. Similarly, the binding of kininogen via its light chain to a surface, as indicated by the binding to the model surface, heparin, did not affect the inhibitory properties of kininogen. The M(r) of high-molecular-weight kininogen was determined to be 83,500 by sedimentation equilibrium measurements, in agreement with the value calculated from amino acid sequence and carbohydrate analysis.

Inhibition of bovine cathepsins L and S by stefins and cystatins

Inhibition of bovine cathepsins L and S by bovine stefin B, human stefins A and B and cystatin C was studied under pseudo-first-order conditions by continuous fluorimetric assay. All inhibitors formed very tight complexes with the enzymes (Ki < or = 29 pM). The binding was reversible (kdiss = 0.52 - 16.7 x 10(-4) s-1) and very fast (kass = 2.8 - 6.2 x 10(7) M-1 S-1). Cystatin C was the strongest inhibitor of the enzymes, but the affinity was too tight to be measured accurately by this method. Consistently weaker inhibition of cathepsin S by all the stefins is apparent due mainly to the higher dissociation rate constants.

Characterization of cystatin C from bovine parotid glands: cysteine proteinase inhibition and antiviral properties

Cystatin C, a low Mr cysteine proteinase inhibitor was isolated from bovine parotid glands by a procedure which includes alkaline treatment of the homogenate, affinity chromatography, gel filtration and ion exchange chromatography. The purified inhibitor has a pl of 8.0 and Mr of 14500. The identity with bovine cystatin C from colostrum was confirmed by N-terminal sequence of the inhibitor and amino acid composition. Cystatin C rapidly (kass = 5.5 x 10(7) M-1s-1) and tightly inhibits papain (Ki = 0.02 nM), whereas its interaction with bovine cathepsin B is substantially weaker (Ki = 4.4 nM). Bovine cystatin C also shows a weak antiviral effect on poliovirus infected human Hela cells.

Oligomeric structure and substrate induced inhibition of human cathepsin C

Cathepsin C has been purified from human kidney by a modified procedure. Human cathepsin C was isolated as pure protein with a pI close to 6.0. The enzyme was shown to have a molecular mass of 200 kDa and to consist of four identical subunits, each composed of three different polypeptide chains, two of them disulfide-bound. Their NH2-terminal amino acid sequences were determined. Two chains showed pronounced similarity with the heavy and light chains of other papain-like cysteine proteinases, whereas the third one corresponded to the prosequence of the enzyme, thus showing that a substantial part of the proregion remains bound in the mature enzyme. The kinetics of substrate hydrolysis deviated substantially from standard Michaelis-Menten kinetics, demonstrating substrate inhibition at higher substrate concentrations. These data are explained by a sequential cooperative interaction model, where an enzyme molecule can bind up to four substrate molecules but where only the binary enzyme-substrate complex is catalytically active. Substrate inhibition was observed over the whole range of pH activity. From the pH activity profile it can be concluded that at least three ionizable groups with pKa values 4.2, 6.8, and 7.7 are involved in substrate hydrolysis. Human cathepsin C thus appears to differ qualitatively from other cysteine proteinases of different origin.

High-affinity binding of two molecules of cysteine proteinases to low-molecular-weight kininogen

Human low-molecular-weight kininogen (LK) was shown by fluorescence titration to bind two molecules of cathepsins L and S and papain with high affinity. By contrast, binding of a second molecule of cathepsin H was much weaker. The 2:1 binding stoichiometry was confirmed by titration monitored by loss of enzyme activity and by sedimentation velocity experiments. The kinetics of binding of cathepsins L and S and papain showed the two proteinase binding sites to have association rate constants kass,1 = 10.7-24.5 x 10(6) M-1 s-1 and kass,2 = 0.83-1.4 x 10(6) M-1 s-1. Comparison of these kinetic constants with previous data for intact LK and its separated domains indicate that the faster-binding site is also the tighter-binding site and is present on domain 3, whereas the slower-binding, lower-affinity site is on domain 2. These results also indicate that there is no appreciable steric hindrance for the binding of proteinases between the two binding sites or from the kininogen light chain.

Elimination of glycosylation heterogeneity affecting heparin affinity of recombinant human antithrombin III by expression of a beta-like variant in baculovirus-infected insect cells

In order to promote homogeneity of recombinant antithrombin III interactions with heparin, an asparagine-135 to alanine substitution mutant was expressed in baculovirus-infected insect cells. The N135A variant does not bear an N-linked oligosaccharide on residue 135 and is therefore similar to the beta isoform of plasma antithrombin. Purified bv.hat3.N135A is homogeneous with respect to molecular mass, charge and elution from immobilized heparin. Second-order rate constants for thrombin and factor Xa inhibition determined in the absence and presence of heparin are in good agreement with values established for plasma antithrombin and these enzymes. Based on far- and near-UV CD, bv.hat3.N135A has a high degree of conformational similarity to plasma antithrombin. Near-UV CD, absorption difference and fluorescence spectroscopy studies indicate that it also undergoes an identical or very similar conformational change upon heparin binding. The Kds of bv.hat3.N135A for high-affinity heparin and pentasaccharide were determined and are in good agreement with those of the plasma beta-antithrombin isoform. The demonstrated similarity of bv.hat3.N135A and plasma antithrombin interactions with target proteinases and heparins suggest that it will be a useful base molecule for investigating the structural basis of antithrombin III heparin cofactor activity.

Regulation of the activity of lysosomal cysteine proteinases by pH-induced inactivation and/or endogenous protein inhibitors, cystatins

The kinetics of pH-induced inactivation of human cathepsins B and L was studied by conventional and stopped-flow methods. The inactivation of both enzymes was found to be an irreversible, first-order process. The inactivation rate constants increased exponentially with pH for both enzymes. From log kinac vs pH plots, 3.0 and 1.7 protons were calculated to be desorbed for pH-induced inactivation of cathepsins L and B. Cathepsin B was thus substantially more stable than cathepsin L (approximately 15-fold at pH 7.0 and 37 degrees C). Cathepsin B was efficiently inhibited by cystatin C at pH 7.4, whereas the inhibition by stefin B and high molecular weight kininogen was only moderate. In contrast, cathepsin L was efficiently inhibited by both chicken cystatin and stefin B at this pH kass approximately 3.3 x 10(7) m-1 s-1).

Identification of bovine stefin A, a novel protein inhibitor of cysteine proteinases

For the first time, three different stefins, A, B and C, have been isolated from a single species. The complete amino acid sequence of bovine stefin A was determined. The inhibitor, with a calculated M(r) of 11,123, consists of 98 amino acid residues. Although it exhibits considerable similarity to human and rat stefin A, some significant differences in inhibition kinetics were found. Bovine stefin A bound tightly and rapidly to cathepsin L (kass = 9.6 x 10(6) M-1.s-1, Ki = 29 pM). The binding to cathepsin H was also rapid (kass = 2.1 x 10(6) M-1.s-1), but weaker (Ki = 0.4 nM) due to a higher dissociation rate constant. In contrast, the binding to cathepsin B was much slower (kass = 1.4 x 10(5) M-1.s-1), but still tight (Ki = 1.9 nM).

Human cathepsin B is a metastable enzyme stabilized by specific ionic interactions associated with the active site

The effect of neutral or alkaline pH on cathepsin B activity and structure was investigated. An irreversible loss of activity, accompanied by large structural changes, was observed at pH > or = 7.0. The high activation energy of 183.5 kJ mol-1, calculated for the inactivation process, is in good agreement with structural changes observed by circular dichroism. Both the pH-induced inactivation and the pH-induced unfolding of cathepsin B were found to be first-order processes, exponentially increasing with increasing pH of the solution. The good agreement of the rate constants of inactivation and unfolding of the enzyme indicates an important structure-function relationship. Cathepsin B was also found to be destabilized both by increasing ionic strength and organic solvent content.

Stefin B, the major low molecular weight inhibitor in ovarian carcinoma

Endogenous cysteine proteinase inhibitors (CPIs) presumably regulate lysosomal cysteine endopeptidases (CPs), such as cathepsins B and L, in vivo. An imbalance between CPs and CPIs in carcinomas, possibly due to impaired inhibition of proteinases, was reported. Ovarian carcinoma contain high levels of Stefin B and about twentyfold less Stefin A compared to normal epithelial tissue. Stefin B was isolated and characterized. We used alkaline treatment, affinity chromatography on Cm-papain Sepharose, followed by gel filtration and ion-exchange chromatography and anti-Stefin B-Sepharose 4B to isolate two major isoforms of Stefin B with pI values 5.9 and 6.5. M(r) of ovarian Stefin B was close to 14,000 as judged by SDS-PAGE and had a blocked N-terminus. It strongly inhibited papain (Ki = 0.11 nM) and cathepsin L (Ki = 0.035 nM), but only moderately cathepsin B (Ki = 130 nM). As these properties are similar to Stefin B from human and bovine origin, as well as to Stefin B from human histiosarcoma, we believe that tumor Stefin B does not differ from normal Stefin B.

Mutations which affect the inhibition of protein phosphatase 2A by simian virus 40 small-t antigen in vitro decrease viral transformation

Three independent point mutations within residues 97 to 103 of the simian virus 40-small-t antigen (small-t) greatly reduced the ability of purified small-t to inhibit protein phosphatase 2A in vitro. These mutations affected the interaction of small-t antigen with the protein phosphatase 2A A subunit translated in vitro, and a peptide from the region identified by these mutations released the A subunit from immune complexes. When introduced into virus, the mutations eliminated the ability of small-t to enhance viral transformation of growth-arrested rat F111 cells. In contrast, the mutant small-t antigens were unimpaired in the transactivation of the adenovirus E2 promoter, an activity which was reduced by a double mutation in small-t residues 43 and 45.

Kinetics of inhibition of bovine cathepsin S by bovine stefin B

The kinetics of the complex formation between bovine cathepsin S and bovine stefin B was studied by conventional and stopped-flow techniques. The inhibition at low inhibitor concentrations was tight and reversible (kass = 5.8 x 10(7) M-1.s-1, kdiss = 4.9 x 10(-4) s-1 at pH 6.0 and 25 degrees C), whereas at higher inhibitor concentrations it was pseudo-irreversible (kass = 6.14 x 10(7) M-1.s-1). The complex was formed directly lacking the fast pre-equilibrium step with the dissociation equilibrium constant of approximately 8 pM. The competitive nature of inhibition was confirmed. The kass was found to be pH-independent between pH 6.0 and 7.5 and decreased at lower or higher pH values in a way that strongly suggests involvement of two ionizable groups in the interaction (pKi = 5.2, pK2 = 8.3). The enzyme-substrate interaction seems to be influenced by different ionizable groups (pKi = 4.4, pK2 = 7.8).

[Reference controlled, randomized double-blind study of the effectiveness of a salbutamol/DNCG DA combination in bronchial hyperreactivity in comparison with salbutamol DA alone (parallel group comparison)]

We examined 20 patients in whom bronchial hyperreactivity and positive inhalative methacholine provocation test (dosage-effect curve) had been known for at least 3 months at the time of study. The patients received randomised either DA Salbutamol/DNCG (0.1 mg Salbutamol and 1.0 mg DNCG/puff) or DA Salbutamol alone (0.1 mg Salbutamol puff). In each case the therapy consisted of 4 x 2 puffs daily. The minimum treatment time was 14 days. The average treatment time was 16 days in both groups. The major aim of the study was to find out whether treatment with the combination preparation in the inhalative methacholine test would lead to a higher provocation dose (PD) for the Rt value and/or sGaw and/or FEV1 representing an alleviation of bronchial hyperreactivity, compared with the pre-examination and with the control group with Salbutamol monotherapy. In addition, the effectivity was to be documented by means of peak-flow values to be measured by the patient himself. The results show in both groups a mild but statistically not significant reduction of the provocation reaction in the inhalative methacholine provocation test in the sense of an improvement in bronchial hyperreactivity. No significant difference between the therapy groups, and especially no superiority of the combination treatment, is evident.

Simian virus 40 small-t antigen binds two zinc ions

Six cysteine residues of the simian virus 40 small-t antigen (small-t) are important for stability of the protein. Stability has been shown to be related to the ability of small-t to bind zinc ions in vitro. Purified small-t expressed either in bacteria or from baculovirus vectors binds two molecules of zinc per molecule of protein. Thus, small-t may resemble GAL4, which contains a Zn(II)2Cys6 binuclear cluster.

Bovine stefin C, a new member of the stefin family

Four low M(r) cysteine proteinase inhibitors with different pI values were isolated from bovine thymus using alkaline activation of the gland homogenate, affinity chromatography on carboxymethyl-papain-Sepharose, gel filtration on Sephadex G-50, ion-exchange chromatography on a DEAE-cellulose column and a fast protein liquid chromatography Mono Q column, and hydrophobic chromatography on a TSK Phenyl-5 PW column. One of the inhibitors was identified both as the monomeric and dimeric forms of stefin B. Two others, called cysteine proteinase inhibitor-1 and cysteine proteinase inhibitor-2, were N terminally blocked and most likely belong to the stefin family. The complete amino acid sequence of the last inhibitor, namely bovine stefin C, was determined. The inhibitor consisted of 101 amino acids and its M(r) was calculated to be 11,546. It exhibits considerable sequence homology with other inhibitors from the stefin family. It was identified as the first tryptophane-containing stefin and it had a prolonged N terminus. The four inhibitors had similar inhibitory activities on cysteine proteinases. They were fast-acting inhibitors of papain and cathepsin L (kass > or = 1.8 x 10(6) M-1 s-1) and formed very tight complexes with the enzymes (Ki < or = 180 pM). In contrast, they were relatively poor inhibitors of cathepsin B (Ki > 100 nM).