Christopher A. Potter

Expression, Purification and Characterisation of Full-length Histidine Protein Kinase RegB from Rhodobacter sphaeroides

The global redox switch between aerobic and anaerobic growth in Rhodobacter sphaeroides is controlled by the RegA/RegB two-component system, in which RegB is the integral membrane histidine protein kinase, and RegA is the cytosolic response regulator. Despite the global regulatory importance of this system and its many homologues, there have been no reported examples to date of heterologous expression of full-length RegB or any histidine protein kinases. Here, we report the amplified expression of full-length functional His-tagged RegB in Escherichia coli, its purification, and characterisation of its properties. Both the membrane-bound and purified solubilised RegB protein demonstrate autophosphorylation activity, and the purified protein autophosphorylates at the same rate under both aerobic and anaerobic conditions confirming that an additional regulator is required to control/inhibit autophosphorylation. The intact protein has similar activity to previously characterised soluble forms, but is dephosphorylated more rapidly than the soluble form (half-life ca 30 minutes) demonstrating that the transmembrane segment present in the full-length RegB may be an important regulator of RegB activity. Phosphotransfer from RegB to RegA (overexpressed and purified from E. coli) by RegB is very rapid, as has been reported for the soluble domain. Dephosphorylation of active RegA by full-length RegB has a rate similar to that observed previously for soluble RegB.

Correlating DWI MRI with pathologic and other features of Jakob-Creutzfeldt disease.

Diffusion-weighted (DWI) magnetic resonance imaging (MRI) is a highly sensitive and specific test for diagnosis of sporadic Jakob-Creutzfeldt disease (sCJD); however, the neuropathologic origin of DWI signal abnormalities including other clinical features has not been well defined. We describe a case of sCJD with brain MRI taken 15 days before death, which provided an opportunity to correlate clinical, electroencephalogram, MRI, and neuropathologic findings to better understand which sCJD-specific neuropathologic changes underlie the DWI abnormalities. Clinical findings correlated well with both electroencephalogram and MRI changes. Neuropathologic analysis showed that hyperintensities on DWI MRI correlated best with the vacuolation score (r=0.78, P=0.0005) and PrPSc load (r=0.77; P=0.0006), followed by reactive astrocytic gliosis (r=0.63, P=0.008). This case provides further evidence that DWI abnormalities correlate well with the clinical features and with PrPSc accumulation and vacuolation.

Assessment of the liver strain among cirrhotic and normal livers using tagged MRI.

To use magnetization tagged magnetic resonance imaging (MRI) (tag‐MRI) to quantify cardiac induced liver strain and compare strain of cirrhotic and normal livers.

Redox-responsive in vitro modulation of the signalling state of the isolated PrrB sensor kinase of Rhodobacter sphaeroides NCIB 8253.

Prr is a global regulatory system that controls a large and diverse range of genes in Rhodobacter sphaeroides in response to changing conditions of environmental redox potential. PrrB is the membrane‐bound sensor kinase and previously we showed that the purified, detergent‐solubilised intact membrane protein is functional in autophosphorylation, phosphotransfer and phosphatase activities. Here we confirm that it also senses and responds directly to its environmental signal, redox potential; strong autophosphorylation of PrrB occurred in response to dithiothreitol (DTT)‐induced reducing conditions (and levels increased in response to a wide 0.1–100 mM DTT range), whilst under oxidising conditions, PrrB exhibited low, just detectable levels of autophosphorylation. The clear response of PrrB to changes in reducing conditions confirmed its suitability for in vitro studies to identify modulators of its phosphorylation signalling state, and was used here to investigate whether PrrB might sense more than one redox‐related signal, such as signals of cell energy status. NADH, ATP and AMP were found to exert no detectable effect on maintenance of the PrrB–P signalling state. By contrast, adenosine diphosphate produced a very strong increase in PrrB–P dephosphorylation rate, presumably through the back‐conversion of PrrB–P to PrrB.

Septic pulmonary emboli from an unusual source

Septic pulmonary embolism, though an uncommon diagnosis, is an important consideration in the differential diagnosis of multiple pulmonary nodules. Septic emboli are now more commonly observed in association with central venous catheters and prosthetic intravascular materials than with intravenous drug use, although the latter continues to be a significant risk factor for septic pulmonary embolism. Chest radiograph findings include multiple, ill-defined, peripheral pulmonary nodules with or without cavitation. Computed tomography is more sensitive and perhaps more specific than radiography. Imaging demonstrates multiple peripheral nodules or consolidation, often in varying stages of cavitation and frequently associated pleural effusion or empyema. Complications may include empyema, pyopneumothorax, and bronchopleural fistula. With early antimicrobial treatment, complete recovery without long-term sequelae is likely for most patients. We present the clinical and imaging findings of a 59-year-old man with septic pulmonary embolism and review the characteristic imaging findings.

Emergent Neuroimaging in the Oncologic and Immunosuppressed Patient

Neuroimaging in the emergency department increasingly involves patients at increased risk for acute neurologic complications from malignancy and immunosuppression, including patients with organ transplantation, diabetes mellitus, treatment of chronic disease, and HIV positivity. These patients are susceptible to the same infections and emergencies as immunocompetent patients, but may present differently with common illnesses and are susceptible to a variety of other diseases. This article reviews important patient risk factors, emergent central nervous system abnormalities, and their imaging findings. Detailed knowledge of risk factors and specific complications in these complex patients is essential for optimal image acquisition, interpretation, diagnosis, and treatment.

Blunt traumatic vascular injuries of the head and neck in the ED

Cerebrovascular injury is increasingly identified in patients presenting after blunt trauma due to the implementation of screening criteria and advances in noninvasive angiographic imaging by CT. The variable latent time before onset of secondary stroke presents a window of opportunity for prevention, reinforcing the importance of detection of asymptomatic patients via screening. Furthermore, the high morbidity and mortality associated with secondary stroke makes it imperative that radiologists recognize these challenging injuries. This article reviews the epidemiology of and the various proposed screening criteria for blunt cerebrovascular injury. The imaging findings of extra- and intracranial vascular injuries, including arterial and venous trauma, are reviewed along with the grading system. Conservative management with anticoagulation has gained favor over the years with intervention restricted to high-grade injuries such as transection and hemodynamically significant arteriovenous fistula. Many of these injuries also evolve over time, with or without anticoagulation, necessitating imaging follow-up.

Core curriculum illustration: invasive fungal sinusitis

This is the 27th installment of a series that will highlight one case per publication issue from the bank of cases available online as part of the American Society of Emergency Radiology (ASER) educational resources. Our goal is to generate more interest in and use of our online materials. To view more cases online, please visit the ASER Core Curriculum and Recommendations for Study online at http://www.erad.org/?page=CCIP_TOC.

BWH emergency radiology-surgical correlation: torsion of Meckel's diverticulum

We present the radiologic findings and intraoperative correlation of a torsed Meckel’s diverticulum leading to small-bowel obstruction in a 65-year-old male without prior abdominal surgery. As this is a rare entity and difficult to diagnose, an understanding of the clinical presentation and radiologic findings correlated with this pathology can help to expedite diagnosis and treatment.