Unique properties of Plasmodium falciparum porphobilinogen deaminase

The hybrid pathway for heme biosynthesis in the malarial parasite proposes the involvement of parasite genome-coded enzymes of the pathway localized in different compartments such as apicoplast, mitochondria, and cytosol. However, knowledge on the functionality and localization of many of these enzymes is not available. In this study, we demonstrate that porphobilinogen deaminase encoded by the Plasmodium falciparum genome (PfPBGD) has several unique biochemical properties. Studies carried out with PfPBGD partially purified from parasite membrane fraction, as well as recombinant PfPBGD lacking N-terminal 64 amino acids expressed and purified from Escherichia coli cells (DeltaPfPBGD), indicate that both the proteins are catalytically active. Surprisingly, PfPBGD catalyzes the conversion of porphobilinogen to uroporphyrinogen III (UROGEN III), indicating that it also possesses uroporphyrinogen III synthase (UROS) activity, catalyzing the next step. This obviates the necessity to have a separate gene for UROS that has not been so far annotated in the parasite genome. Interestingly, DeltaPfP-BGD gives rise to UROGEN III even after heat treatment, although UROS from other sources is known to be heat-sensitive. Based on the analysis of active site residues, a DeltaPfPBGDL116K mutant enzyme was created and the specific activity of this recombinant mutant enzyme is 5-fold higher than DeltaPfPBGD. More interestingly, DeltaPfPBGDL116K catalyzes the formation of uroporphyrinogen I (UROGEN I) in addition to UROGEN III, indicating that with increased PBGD activity the UROS activity of PBGD may perhaps become rate-limiting, thus leading to non-enzymatic cyclization of preuroporphyrinogen to UROGEN I. PfPBGD is localized to the apicoplast and is catalytically very inefficient compared with the host red cell enzyme.     

Comparison of the accuracy of disk diffusion zone diameters obtained by manual zone measurements to that by automated zone measurements to determine antimicrobial susceptibility

Although a variety of techniques are available for antimicrobial susceptibility testing, disk diffusion methods remain the most widely used. We compared the accuracy of disk diffusion zone diameters as obtained by manual zone measurements in a low resource country (Indonesia) to that by automated zone measurements (Oxoid aura image system) in a high resource setting (the Netherlands) to determine susceptibility categories (sensitive, intermediate susceptible or resistant). A total of 683 isolates were studied, including 294 Staphylococcus aureus, 195 Escherichia coli and 194 other Enterobacteriaceae. Antimicrobial agents included tetracycline, oxacillin, gentamicin, erythromycin, trimethoprim/sulfamethoxazole and chloramphenicol for S. aureus and ampicillin, gentamicin, cefotaxime, ciprofloxacin, trimethoprim/sulfamethoxazole, and chloramphenicol for E. coli and other Enterobacteriaceae. Of the 4098 drug-organism combinations, overall category agreement (CA), major discrepancy (MD) and minor discrepancy (mD) between the two methods were 82.4% (3379/4098), 6.0% (244/4098) and 11.6% (475/4098), respectively. One hundred and sixty three of 244 MDs were resolved using reference broth microdilution method. Overall very major error (VME), major error (ME) and minor error (mE) of manual zone measurement were 28.8%, 45.4% and 4.9%, respectively and for the aura image system 4.9%, 16.0% and 4.9%, respectively. The results of this study indicate that the disk diffusion method with manual zone measurement in Indonesia is reliable for susceptibility testing. The use of an automated zone reader, such as the aura image system, will reduce the number of errors, and thus improve the accuracy of susceptibility test results for medically relevant bacteria.     

Nutritional Differences between Two Orangutan Habitats: Implications for Population Density

Bottom-up regulatory factors have been proposed to exert a strong influence on mammalian population density. Studies relating habitat quality to population density have typically made comparisons among distant species or communities without considering variation in food quality among localities. We compared dietary nutritional quality of two Bornean orangutan populations with differing population densities in peatland habitats, Tuanan and Sabangau, separated by 63 km. We hypothesized that because Tuanan is alluvial, the plant species included in the orangutan diet would be of higher nutritional quality compared to Sabangau, resulting in higher daily caloric intake in Tuanan. We also predicted that forest productivity would be greater in Tuanan compared to Sabangau. In support of these hypotheses, the overall quality of the diet and the quality of matched dietary items were higher in Tuanan, resulting in higher daily caloric intake compared to Sabangau. These differences in dietary nutritional quality may provide insights into why orangutan population density is almost two times greater in Tuanan compared to Sabangau, in agreement with a potentially important influence of diet quality on primate population density.     

Exome Capture Reveals ZNF423 and CEP164 Mutations, Linking Renal Ciliopathies to DNA Damage Response Signaling

Nephronophthisis-related ciliopathies (NPHP-RC) are degenerative recessive diseases that affect kidney, retina, and brain. Genetic defects in NPHP gene products that localize to cilia and centrosomes defined them as "ciliopathies." However, disease mechanisms remain poorly understood. Here, we identify by whole-exome resequencing, mutations of MRE11, ZNF423, and CEP164 as causing NPHP-RC. All three genes function within the DNA damage response (DDR) pathway. We demonstrate that, upon induced DNA damage, the NPHP-RC proteins ZNF423, CEP164, and NPHP10 colocalize to nuclear foci positive for TIP60, known to activate ATM at sites?of DNA damage. We show that knockdown of CEP164 or ZNF423 causes sensitivity to DNA damaging agents and that cep164 knockdown in zebrafish results in dysregulated DDR and an NPHP-RC phenotype. Our findings link degenerative diseases of the kidney and retina, disorders of increasing prevalence, to mechanisms of DDR. PAPERFLICK:     

Structural and biological basis of CTL escape in coronavirus-infected mice

Cytotoxic T lymphocyte escape occurs in many human infections, as well as mice infected with the JHM strain of mouse hepatitis virus, which exhibit CTL escape variants with mutations in a single epitope from the spike glycoprotein (S510). In all CTL epitopes prone to escape, only a subset of all potential variants is generally detected, even though many of the changes that are not selected would result in evasion of the T cell response. It is postulated that these unselected mutations significantly impair virus fitness. To define more precisely the basis for this preferential selection, we combine x-ray crystallographic studies of the MHC class I (D(b))/S510 complexes with viral reverse genetics to identify a prominent TCR contact residue (tryptophan at position 4) prone to escape mutations. The data show that a mutation that is commonly detected in chronically infected mice (tryptophan to arginine) potently disrupts the topology of the complex, explaining its selection. However, other mutations at this residue, which also abrogate the CTL response, are never selected in vivo even though they do not compromise virus fitness in acutely infected animals or induce a significant de novo CTL response. Thus, while structural analyses of the S510/D(b) complex provide a strong basis for why some CTL escape variants are selected, our results also show that factors other than effects on virus fitness limit the diversification of CD8 T cell epitopes.     

Unusual presentations of a severe type 2 leprosy reaction mimicking sepsis induced by helminth infection

We describe an unusual case of type 2 leprosy reaction (T2R) with septic shock–like features induced by helminth infection in a 31-year-old Moluccan male patient with a history of completed treatment of WHO multidrug therapy (MDT)–multibacillary (MB) regimen 2 years before admission. During the course of illness, the patient had numerous complications, including septic shock, anemia, and disseminated intravascular coagulation (DIC). Nevertheless, antibiotic therapies failed to give significant results, and the source of infection could not be identified. Helminth infection was subsequently revealed by endoscopic examination followed by parasitological culture. Resolution of symptoms and normal level of organ function–specific markers were resolved within 3 days following anthelmintic treatment. This report demonstrated the challenge in the diagnosis and treatment of severe T2R. Given that helminth infections may trigger severe T2R that mimics septic shock, health professionals need to be aware of this clinical presentation, especially in endemic regions of both diseases.

Type 2 leprosy reaction (T2R) is a type III hypersensitivity reaction that can occur in people with lepromatous or borderline lepromatous leprosy before, during, or after completion of multidrug therapy (MDT). Its clinical manifestations are highly variable, which can be limited to the skin or accompanied by systemic disruption [1,2]. Uncommonly, it may also present with fever, hypotension, and tachycardia that mimic septic shock [3]. Helminth infections have been demonstrated to modulate the host immune response and induce leprosy reaction [4]. While concurrent helminth infections may benefit true sepsis by preventing exaggerated inflammation and severe pathology [5], treating helminth coinfection contributed directly to the dramatic improvement of the patient’s clinical and laboratory outcomes in this report.     

Determination of Cloretazine (VNP40101M) and its active metabolite (VNP4090CE) in human plasma by liquid chromatography electrospray tandem mass spectrometry (LC-ESI-MS/MS)

A sensitive method for the determination of Cloretazine (VNP40101M) and its metabolite (VNP4090CE) with an internal standard (ISTD) in human plasma was developed using high-performance liquid chromatographic separation with tandem mass spectrometric detection. Acidified plasma samples (500 microL) were prepared using solid phase extraction (SPE) columns, and 25 microL of the reconstituted sample was injected onto an Ascentis C18 HPLC column (3 microm, 5 cmx2.1 mm) with an isocratic mobile phase. Analytes were detected with an API-3000 LC-MS/MS System at unit (Q1) and low (Q3) resolution in negative multiple reaction monitoring mode: m/z 249.0 (precursor ion) to m/z 114.9 (product ion) for both Cloretazine (at 3.64 min) and VNP4090CE (at 2.91 min), and m/z 253.0 (precursor ion) to m/z 116.9 (product ion) for the ISTD. The mean recovery for Cloretazine (VNP40101M) and its metabolite (VNP4090CE) was greater than 87% with a lower limit of quantification of 1.0 ng/mL for Cloretazine (S/N=9.7, CV相似文献