Novel kinase platform for the validation of the anti-tubercular activities of Pelargonium sidoides (Geraniaceae)

Background

Pelargonium sidoides is an important traditional medicine in South Africa with a well-defined history of both traditional and documented use of an aqueous-ethanolic formulation of the roots of P. sidoides (EPs 7630), which is successfully employed for the treatment of respiratory tract infections. There is also historical evidence of use in the treatment of tuberculosis. The aim of this study was to develop a platform of Mycobacterium tuberculosis (Mtb) kinase enzymes that may be used for the identification of therapeutically relevant ethnobotanical extracts that will allow drug target identification, as well as the subsequent isolation of the active compounds.

Results

Mtb kinases, Nucleoside diphosphokinase, Homoserine kinase, Acetate kinase, Glycerol kinase, Thiamine monophosphate kinase, Ribokinase, Aspartokinase and Shikimate kinase were cloned, produced in Escherichia coli and characterized. HPLC-based assays were used to determine the enzyme activities and subsequently the inhibitory potentials of varying concentrations of a P. sidoides extract against the produced enzymes. The enzyme activity assays indicated that these enzymes were active at low ATP concentrations. The 50% inhibitory concentration (IC₅₀) of an aqueous root extract of P. sidoides against the kinases indicated SK has an IC₅₀ of 1.2 μg/ml and GK 1.4 μg/ml. These enzyme targets were further assessed for compound identification from the P. sidoides literature.

Conclusion

This study suggests P. sidoides is potentially a source of anti-tubercular compounds and the Mtb kinase platform has significant potential as a tool for the subsequent screening of P. sidoides extracts and plant extracts in general, for compound identification and elaboration by selected extract target inhibitor profiling.

Analyzing the molecular mechanism of lipoprotein localization in Brucella

Bacterial lipoproteins possess diverse structure and functionality, ranging from bacterial physiology to pathogenic processes. As such many lipoproteins, originating from Brucella are exploited as potential vaccines to countermeasure brucellosis infection in the host. These membrane proteins are translocated from the cytoplasm to the cell membrane where they are anchored peripherally by a multifaceted targeting mechanism. Although much research has focused on the identification and classification of Brucella lipoproteins and their potential use as vaccine candidates for the treatment of Brucellosis, the underlying route for the translocation of these lipoproteins to the outer surface of the Brucella (and other pathogens) outer membrane (OM) remains mostly unknown. This is partly due to the complexity of the organism and evasive tactics used to escape the host immune system, the variation in biological structure and activity of lipoproteins, combined with the complex nature of the translocation machinery. The biosynthetic pathway of Brucella lipoproteins involves a distinct secretion system aiding translocation from the cytoplasm, where they are modified by lipidation, sorted by the lipoprotein localization machinery pathway and thereafter equipped for export to the OM. Surface localized lipoproteins in Brucella may employ a lipoprotein flippase or the β-barrel assembly complex for translocation. This review provides an overview of the characterized Brucella OM proteins that form part of the OM, including a handful of other characterized bacterial lipoproteins and their mechanisms of translocation. Lipoprotein localization pathways in gram negative bacteria will be used as a model to identify gaps in Brucella lipoprotein localization and infer a potential pathway. Of particular interest are the dual topology lipoproteins identified in Escherichia coli and Haemophilus influenza. The localization and topology of these lipoproteins from other gram negative bacteria are well characterized and may be useful to infer a solution to better understand the translocation process in Brucella.

The role of the C8 proton of ATP in the catalysis of shikimate kinase and adenylate kinase

Background

It has been demonstrated that the adenyl moiety of ATP plays a direct role in the regulation of ATP binding and/or phosphoryl transfer within a range of kinase and synthetase enzymes. The role of the C8-H of ATP in the binding and/or phosphoryl transfer on the enzyme activity of a number of kinase and synthetase enzymes has been elucidated. The intrinsic catalysis rate mediated by each kinase enzyme is complex, yielding apparent K_M values ranging from less than 0.4 μM to more than 1 mM for ATP in the various kinases. Using a combination of ATP deuterated at the C8 position (C8D-ATP) as a molecular probe with site directed mutagenesis (SDM) of conserved amino acid residues in shikimate kinase and adenylate kinase active sites, we have elucidated a mechanism by which the ATP C8-H is induced to be labile in the broader kinase family. We have demonstrated the direct role of the C8-H in the rate of ATP consumption, and the direct role played by conserved Thr residues interacting with the C8-H. The mechanism by which the vast range in K_M might be achieved is also suggested by these findings.

Results

We have demonstrated the mechanism by which the enzyme activities of Group 2 kinases, shikimate kinase (SK) and adenylate kinase 1 (AK1), are controlled by the C8-H of ATP. Mutations of the conserved threonine residues associated with the labile C8-H cause the enzymes to lose their saturation kinetics over the concentration range tested. The relationship between the role C8-H of ATP in the reaction mechanism and the ATP concentration as they influence the saturation kinetics of the enzyme activity is also shown. The SDM clearly identified the amino acid residues involved in both the catalysis and regulation of phosphoryl transfer in SK and AK1 as mediated by C8H-ATP.

Conclusions

The data outlined serves to demonstrate the “push” mechanism associated with the control of the saturation kinetics of Group 2 kinases mediated by ATP C8-H. It is therefore conceivable that kinase enzymes achieve the observed 2,500-fold variation in K_M through a combination of the various conserved “push” and “pull” mechanisms associated with the release of C8-H, the proton transfer cascades unique to the class of kinase in question and the resultant/concomitant creation of a pentavalent species from the γ-phosphate group of ATP. Also demonstrated is the interplay between the role of the C8-H of ATP and the ATP concentration in the observed enzyme activity. The lability of the C8-H mediated by active site residues co-ordinated to the purine ring of ATP therefore plays a significant role in explaining the broad K_M range associated with kinase steady state enzyme activities.

The role of the C8 proton of ATP in the regulation of phosphoryl transfer within kinases and synthetases

BACKGROUND

The kinome comprises functionally diverse enzymes, with the current classification indicating very little about the extent of conserved regulatory mechanisms associated with phosphoryl transfer. The apparent Km of the kinases ranges from less than 0.4 μM to in excess of 1000 μM for ATP. It is not known how this diverse range of enzymes mechanistically achieves the regulation of catalysis via an affinity range for ATP varying by three-orders of magnitude.

RESULTS

We have demonstrated a previously undiscovered mechanism in kinase and synthetase enzymes where the overall rate of reaction is regulated via the C8-H of ATP. Using ATP deuterated at the C8 position (C8D-ATP) as a molecular probe it was shown that the C8-H plays a direct role in the regulation of the overall rate of reaction in a range of kinase and synthetase enzymes. Using comparative studies on the effect of the concentration of ATP and C8D-ATP on the activity of the enzymes we demonstrated that not only did C8D-ATP give a kinetic isotope effect (KIE) but the KIE's obtained are clearly not secondary KIE effects as the magnitude of the KIE in all cases was at least 2 fold and in most cases in excess of 7 fold.

CONCLUSIONS

Kinase and synthetase enzymes utilise C8D-ATP in preference to non-deuterated ATP. The KIE obtained at low ATP concentrations is clearly a primary KIE demonstrating strong evidence that the bond to the isotopically substituted hydrogen is being broken. The effect of the ATP concentration profile on the KIE was used to develop a model whereby the C8H of ATP plays a role in the overall regulation of phosphoryl transfer. This role of the C8H of ATP in the regulation of substrate binding appears to have been conserved in all kinase and synthetase enzymes as one of the mechanisms associated with binding of ATP. The induction of the C8H to be labile by active site residues coordinated to the ATP purine ring may play a significant role in explaining the broad range of Km associated with kinase enzymes.

Knowledge is payment: understanding state prompt-payment laws

Faced with lagging receivables, hospitals across the country increasingly are suing delinquent payers to obtain payment. States have responded to the provider payment crisis by enacting and enforcing a rash of new laws requiring payers to pay claims within strict time frames or face steep penalties. To take advantage of the protection afforded by these laws, providers need to be aware of prompt-payment statutes in states in which they provide care, in which their patients live, and in which their payers are located. By becoming aware of their rights and obligations under these laws, providers can use the prompt-payment regulations proactively to avoid payment backlogs without resorting to litigation.

The government's best offense is deference: the decision of the Supreme Court in Shalala v. Guernsey Memorial Hospital

The United States Supreme Court agreed with the Secretary of Health and Human Services that Guernsey Memorial Hospital's advance refunding transaction costs would be subject to a medicare reimbursement policy that is not based upon generally accepted accounting principles. According to the sharp dissent in this case, this policy, set forth in a manual provision, contradicts federal regulations.

Medicare and GAAP: understanding the decision of the Sixth Circuit in Guernsey Memorial Hospital v. Secretary of Health and Human Services

The Medicare Act entitles qualified providers to reimbursement for the "reasonable cost" of furnishing hospital services to Medicare beneficiaries. The Sixth Circuit's decision in Guernsey Memorial Hospital demonstrates the tension between generally accepted accounting principles and Medicare reimbursement principles.

Serial exercise testing after coronary artery bypass surgery

To determine the duration of functional benefit from coronary bypass surgery, 111 patients with angina pectoris were serially evaluated by standard exercise testing prior to and for up to 4 years after surgery. Exercise testing 6 to 18 months after surgery showed greater heart rate-blood pressure product at peak work load, improved work capacity, and less symptomatic and electrocardiographic evidence of ischemia than was demonstrated preoperatively. Twenty patients were tested 37 to 48 months postoperatively and showed improved exercise performance in comparison with preoperative results, but the frequency of positive tests during this period no longer differed. Thus, improved exercise performance appears to persist for at least 4 years after coronary bypass surgery.

Expulsion of Nippostrongylus brasiliensis by mice deficient in mast cells

Expulsion of the intestinal helminth, Nippostrongylus brasiliensis, occurs spontaneously about 2 weeks after a primary infection of rats and mice. Cellular changes in the small intestine coincident with the period of expulsion have suggested several mechanisms by which this 'self-cure' may be effected. Local anaphylaxis was proposed as a possible means of parasite clearance; this hypothesis has been supported by the demonstration of specific reaginic antibody production and jejunal mast cell accumulation in infected animals. In addition, increased mucus secretion and more recently, goblet cell proliferation in the jejunal mucosa of rats have been noted and considered as potentially important in mediating the self-cure reaction. The data presented below indicate that in the absence of demonstrable mast cells, the course of a primary infection with this parasite is unchanged; however, they are supportive of a role for globlet cells in the self-cure reaction.

Decussion geometrics in the goldfish nervous system: correlation with probability of survival

In the goldfish, the optic nerve decussation occurs without intermingling of fibers from the two eyes. In two-thirds of juvenile and adult specimens, the left optic nerve is dorsal at the midline. In about 60% of the specimens, the decussation of Mauthner's neuron also has a left-dorsal-to-right (L/R) configuration. Concordance for decussation geometry is greater than 80%, with smaller specimens accounting for a disproportionate number of discordant cases. In embryos and very young larvae, the L/R configuration occurs in slightly less than 50% of optic chiasmata and in slightly more than 50% of Mauthner's cell chiasmata, and there is no significant tendency toward concordance. However, larval specimens that survive 1 month after hatching are markedly skewed toward adult decussation patterns and somewhat skewed toward concordance. These observations, together with results of cannibalization and predation experiments, suggest that the adult population pattern can be achieved through selection pressures against discordant individuals and, perhaps separately, against individuals with right-dorsal-to-left (R/L) chiasmatic configurations. Decussation patterns correlate with embryonic postures, larval orientation preferences, and growth rates after hatching, which may themselves serve as a basis for selection.

Histological evidence for direct connections between the optic lobes of the cockroach Leucophaea maderae

Heretofore, descriptions of direct interconnections between insect optic lobes have been based on histological examinations of normal brains or on inference from electrophysiological or behavioral data. We present here what we believe to be the first demonstration of such monosynaptic connections by techniques of experimental neuroanatomy. Twenty-four to 39 h after extirpation of the left optic lobe, degenerating axons and axon terminals, as silvered by a modified Nauta technique, were abundant in the central portion of the medulla of the right optic lobe. The periphery of the medulla was free of argyrophilic debris as were the lobula and lamina. The distribution of neuronal somata with processes terminating in the the left optic lobe was established by retrograde axonal transport of horseradish peroxidase injected into the left lobe and by the development of distinctive perinuclear rings of RNA (a 'chromatolytic' reaction) by some cells within 1-2 weeks following amputation of the left lobe. Both techniques revealed distinct clusters of cells in the anteroventral and posterior regions of the right optic lobe, and in the medial portion of the right protocerebrum. The cells which interconnect the two optic lobes may be involved not only in the bilateral representation of visual information, but also in the coordination of optic lobe pacemakers which control a circadian rhythm of locomotory activity.