The Trypanosoma cruzi Virulence Factor Oligopeptidase B (OPBTc) Assembles into an Active and Stable Dimer

Oligopeptidase B, a processing enzyme of the prolyl oligopeptidase family, is considered as an important virulence factor in trypanosomiasis. Trypanosoma cruzi oligopeptidase B (OPBTc) is involved in host cell invasion by generating a Ca2+-agonist necessary for recruitment and fusion of host lysosomes at the site of parasite attachment. The underlying mechanism remains unknown and further structural and functional characterization of OPBTc may help clarify its physiological function and lead to the development of new therapeutic molecules to treat Chagas disease. In the present work, size exclusion chromatography and analytical ultracentrifugation experiments demonstrate that OPBTc is a dimer in solution, an association salt and pH-resistant and independent of intermolecular disulfide bonds. The enzyme retains its dimeric structure and is fully active up to 42°C. OPBTc is inactivated and its tertiary, but not secondary, structure is disrupted at higher temperatures, as monitored by circular dichroism and fluorescence spectroscopy. It has a highly stable secondary structure over a broad range of pH, undergoes subtle tertiary structure changes at low pH and is less stable under moderate ionic strength conditions. These results bring new insights into the structural properties of OPBTc, contributing to future studies on the rational design of OPBTc inhibitors as a promising strategy for Chagas disease chemotherapy

Experience with low-dose replacement therapy in the initial management of severe pediatric acquired primary hypothyroidism.

Rapid hormonal replacement of children with severe primary hypothyroidism frequently results in irritability and poor concentration. To alleviate these problems we have been using initial low-dose thyroxine treatment, building up to a final dose in an incremental manner over 4 1/2 to 6 months. Because of concern this regimen may compromise growth, we reviewed our experience treating 14 children and adolescents. For the 10 patients with remaining growth potential, 5 to 7 month growth velocity from the onset of treatment was 8.5 +/- 1.9 cm/year (range 5.7-10.9), and 5 to 7 month growth velocity z-score 1.5 +/- 1.7 (range 0.2-4.9). For the entire group, the thyroxine dose required to normalize TSH was 1.6 +/- 0.74 microgram/kg (range 0.9-3.4) or 60.7 +/- 18.9 micrograms/m2 (range 37.5-97.7). Based on the 5 to 7 month z-score, we conclude that satisfactory growth can be achieved on this regimen despite biochemical hypothyroidism. Thyroxine doses required to induce initial euthyroidism are lower than previously proposed