Crystal structure and biophysical characterization of IspD from Burkholderia thailandensis and Mycobacterium paratuberculosis.

The methylerythritol phosphate (MEP) pathway is a metabolic pathway that produces the isoprenoids isopentyl pyrophosphate and dimethylallyl pyrophosphate. Notably, the MEP pathway is present in bacteria and not in mammals, which makes the enzymes of the MEP pathway attractive targets for discovering new anti-infective agents due to the reduced chances of off-target interactions leading to side effects. There are seven enzymes in the MEP pathway, the third of which is IspD. Two crystal structures of Burkholderia thailandensis IspD (BtIspD) were determined: an apo structure and that of a complex with cytidine triphosphate (CTP). Comparison of the CTP-bound BtIspD structure with the apo structure revealed that CTP binding stabilizes the loop composed of residues 13-19. The apo structure of Mycobacterium paratuberculosis IspD (MpIspD) is also reported. The melting temperatures of MpIspD and BtIspD were evaluated by circular dichroism. The moderate Tm values suggest that a thermal shift assay may be feasible for future inhibitor screening. Finally, the binding affinity of CTP for BtIspD was evaluated by isothermal titration calorimetry. These structural and biophysical data will aid in the discovery of IspD inhibitors.

Undifferentiated Hepatic Sarcoma: A Rare Case.

Primary hepatic undifferentiated pleomorphic sarcoma (UPS) is a rare malignant mesenchymal tumor with a nonspecific clinical and radiologic presentation. Primary hepatic UPS is often a diagnosis of exclusion made by multiple immunohistological testing that rules out hepatic, hematologic, neural, and epithelial origin. Stains for mesenchymal origin are usually the only positive stain and do not demonstrate evidence of specific mesenchymal cell differentiation. We report a case of a 56-year-old male with no significant past medical history that presented with complaint of epigastric abdominal pain of six months duration. A computed tomography (CT) scan of the abdomen and pelvis exhibited numerous hepatic masses involving right and left hepatic lobe. A CT-guided core needle biopsy discovered undifferentiated/pleomorphic sarcoma. Histomorphology showed spindle cell neoplasm without recognizable hepatic tissue. Immunohistochemistry (IHC) stains were positive for smooth muscle actin (SMA) but failed to establish a more specific histogenesis. Furthermore, IHC stains revealed spindle neoplastic cells with focal and patchy positive h-caldesmon (approximately 10-15% of neoplastic cells), and negative for desmin. Given these results, the diagnosis of undifferentiated/pleomorphic sarcoma was established. It is imperative to consider UPS in the differential diagnosis of large liver lesions without evidence of differentiation. Early identification of this rare tumor can prevent the possibility of distant metastasis and improve survival among patients.