The factor VII zymogen structure reveals reregistration of beta strands during activation.

BACKGROUND: Coagulation factor VIIa (FVIIa) contains a Trypsin-like serine protease domain and initiates the cascade of proteolytic events leading to Thrombin activation and blood clot formation. Vascular injury allows formation of the complex between circulating FVIIa and its cell surface bound obligate cofactor, Tissue Factor (TF). Circulating FVIIa is nominally activated but retains zymogen-like character and requires TF in order to complete the zymogen-to-enzyme transition. The manner in which TF exerts this effect is unclear. The structure of TF/FVIIa is known. Knowledge of the zymogen structure is helpful for understanding the activation transition in this system. RESULTS: The 2 A resolution crystal structure of a zymogen form of FVII comprising the EGF2 and protease domains is revealed in a complex with the exosite binding inhibitory peptide A-183 and a vacant active site. The activation domain, which includes the N terminus, differs in ways beyond those that are expected for zymogens in the Trypsin family. There are large differences in the TF binding region. An unprecedented 3 residue shift in registration between beta strands B2 and A2 in the C-terminal beta barrel and hydrogen bonds involving Glu154 provide new insight into conformational changes accompanying zymogen activation, TF binding, and enzymatic competence. CONCLUSIONS: TF-mediated allosteric control of the activity of FVIIa can be rationalized. The reregistering beta strand connects the TF binding region and the N-terminal region. The zymogen registration allows H bonds that prevent the N terminus from attaining a key salt bridge with the active site. TF binding may influence an equilibrium by selecting the enzymatically competent registration.

Pediatric tuberculosis: an update.

The incidence of tuberculous infection and disease in children has risen significantly over the last decade. The management of TB has become more complicated by the changing epidemiology of this disease and the emergence of resistant MTB. Many new recommendations have recently been made to address these issues. It is crucial that pediatricians become familiar with this disease again and have a good working knowledge of pediatric TB.

Infectivity of Legionella pneumophila mip mutant for alveolar epithelial cells.

Legionella pneumophila can invade and grow within explanted alveolar epithelial cells. Given its potential clinical significance, an examination of the molecular basis of epithelial cell infection was initiated. The mip gene encodes a 24-kilodalton surface protein that promotes macrophage infection and virulence. To determine whether this gene is required for pneumocyte infection, we tested a strain bearing a mip null mutation for its ability to infect both explanted type II cells and type I-like cell lines. For infection of type II cells, the infective dose 50% for the Mip-strain was 25-fold higher than an isogenic Mip+ strain. Type I cell monolayers infected with the mutant for 3 days yielded approximately 50-fold fewer bacteria than did monolayers infected with the parental strain. These data indicate that Mip enhances infection of pneumocytes and that L. pneumophila employs some of the same genes (mechanisms) to infect epithelial cells and macrophages.

Candidemia in a pediatric population.

Candidemia results in a mortality of > 50% among adults, but data on children with candidemia are limited. We reviewed 70 episodes of pediatric candidemia that occurred between January 1988 and October 1992. Of these episodes, 53% were caused by Candida albicans, 24% were caused by Candida parapsilosis, 16% were caused by Candida tropicalis, and 3% were caused by Candida krusei. Twenty-five percent of the patients were premature infants. Other underlying conditions included malignancy (15%); cardiac disease (14%); and short-gut syndrome (14%). A central venous catheter was in place during 61 (87%) of 70 episodes. Candiduria preceded candidemia in only 4 (8%) of 52 patients. The overall mortality rate was 19%; 36% of those with intravenous catheters that were not removed within 3 days died, whereas none of the patients from whom catheters were removed within 3 days died (P < .0001). Only two survivors had complications. Therapy with amphotericin B (with or without flucytosine) was administered to 74% of these patients. Seventeen patients were not treated medically; all were immunocompetent and survived. Of these patients, 15 were > 2 months of age; 14 had candidemia for < or = 2 days; and 15 had an intravenous catheter removed within 2 days of the onset of candidemia. No patient stopped receiving amphotericin B because of side effects. The results of this study suggest the following: that mortality associated with candidemia is lower among children than among adults; that failure to remove the indwelling intravenous catheter usually results in a poor outcome; that candiduria rarely precedes candidemia in children; and that amphotericin B is well tolerated by children.

Timely diagnosis of congenital infections.

The acronym TORCH has served to increase awareness of congenital infections; however, this collective term suggests that the clinical manifestations of congenital infections are not distinguishable by pathogen. Although some clinical features may be common to several of these infections, a congenital infection caused by one pathogen generally can be distinguished from infection caused by another pathogen on a clinical basis. Pediatricians need to be aware of the prominent features of each congenital infection rather than to consider them collectively. This article focuses on the prominent features of the more common congenital infections, suggests a specific diagnostic approach, and reviews the available therapeutic strategies.

Ventriculoperitoneal shunt infections with gram-negative bacteria.

Infection causes major morbidity and mortality in patients with cerebrospinal fluid (CSF) shunts. The prognosis of CSF shunt infections caused by Gram-negative bacteria (GNB) has been thought to be particularly poor. The authors reviewed all GNB shunt infections treated at Children's Memorial Hospital from January 1986 to January 1990 (n = 23). Of these infections 20 (87%) occurred within 4 weeks after shunt revision (median, 10 days). The most frequent symptoms were fever, lethargy, and irritability; the illness was not severe in the majority of these patients. Escherichia coli was isolated from 12 of 23 patients (52%), Klebsiella pneumoniae from 5 (22%), and mixed GNB from 3 (13%) patients. Initial treatment always included immediate shunt removal, externalized ventricular drainage, and intravenous antibiotics. Extraventricular drainage revision and/or intraventricular antibiotics were required in four patients whose CSF cultures were persistently positive for GNB. At admission, these patients had CSF glucose levels of < 10 mg/dl and CSF positive for GNB by Gram's stain. The overall cure rate was 100%, and no recurrence was observed; however, a subsequent infection with a different organism developed in four patients. Only 2 of 19 patients (11%) who were followed up suffered apparent CNS damage. One patient died of unrelated causes shortly after treatment. Our findings indicate that 1) patients with GNB CSF shunt infections often appear relatively well at presentation; 2) CSF positive for GNB by Gram's stain and very low CSF glucose levels predict continued positive CSF cultures, despite appropriate antibiotic therapy; and 3) GNB CSF shunt infections can be successfully treated by prompt shunt removal, extraventricular drainage, and intravenous antibiotics.(ABSTRACT TRUNCATED AT 250 WORDS)

Preconditioning methods for improved convergence rates in iterative reconstructions.

Because of the characteristics of the tomographic inversion problem, iterative reconstruction techniques often suffer from poor convergence rates-especially at high spatial frequencies. By using preconditioning methods, the convergence properties of most iterative methods can be greatly enhanced without changing their ultimate solution. To increase reconstruction speed, spatially invariant preconditioning filters that can be designed using the tomographic system response and implemented using 2-D frequency-domain filtering techniques have been applied. In a sample application, reconstructions from noiseless, simulated projection data, were performed using preconditioned and conventional steepest-descent algorithms. The preconditioned methods demonstrated residuals that were up to a factor of 30 lower than the assisted algorithms at the same iteration. Applications of these methods to regularized reconstructions from projection data containing Poisson noise showed similar, although not as dramatic, behavior.

SPRINT II: a second generation single photon ring tomograph.

SPRINT II is a stationary detector ring tomograph designed for brain imaging. Eleven two-dimensional sodium iodide camera modules that use maximum-likelihood position logic are arranged in a 50-cm-diameter ring with a scintillator packing fraction of 96%. A 34-cm-diameter rotating lead aperture ring containing either 10 or 12 slits is used for in-plane collimation, while the z-axis collimator is constructed of parallel lead foil rings. The field of view is 22 cm in diameter by 12 cm long. Sensitivity is 10 count/s/muCi for an on-axis (99m)Tc point source and 8500 count/s/muCi/cm(3) for 19.8-cm-diameter by 6.2-cm-long cylindrical source. Longitudinal resolution is 10 mm FWHM, and in-plane resolution varies from 8 mm FWHM on-axis to 5 mm FWHM at a radius of 9 cm. Performance results are presented.

Performance evaluation of SPRINT, a single photon ring tomography for brain imaging.

SPRINT, a prototype single photon tomograph, has been designed primarily for high-resolution brain imaging in humans with I-123-labeled compounds such as iodoamphetamine, hydroxyiodopropyldiamine (HIPDM), and iodobenzene (IBZ). SPRINT uses a ring of stationary, discrete Nal detectors, and fan-beam sampling is accomplished with a rotating eight-slit aperture ring that acquires a complete projection set in 1/8 revolution. In-plane and cross-plane resolutions are 8mm and 10mm FWHM, respectively, measured on axis. Sensitivity with an 18% energy window is 1000 cprs per microCi/cc for Tc-99m in a 20 cm diameter phantom. A detailed evaluation of system performance has been completed, and preliminary human brain blood flow images have been obtained using HIPDM.