Design, synthesis, and characterization of a photoactivatable flavocytochrome molecular maquette

We report the construction of a synthetic flavo-heme protein that incorporates two major physiological activities of flavoproteins: light activation of flavin analogous to DNA photolyase and rapid intramolecular electron transfer between the flavin and heme cofactors as in several oxidoreductases. The functional tetra-alpha-helix protein comprises two 62-aa helix-loop-helix subunits. Each subunit contains a single cysteine to which flavin (7-acetyl-10-methylisoalloxazine) is covalently attached and two histidines appropriately positioned for bis-his coordination of heme cofactors. Both flavins and hemes are situated within the hydrophobic core of the protein. Intramolecular electron transfer from flavosemiquinone generated by photoreduction from a sacrificial electron donor in solution was examined between protoporphyrin IX and 1-methyl-2-oxomesoheme XIII. Laser pulse-activated electron transfer from flavin to meso heme occurs on a 100-ns time scale, with a favorable free energy of approximately -100 meV. Electron transfer from flavin to the lower potential protoporphyrin IX, with an unfavorable free energy, can be induced after a lag phase under continuous light illumination. Thus, the supporting peptide matrix provides an excellent framework for the positioning of closely juxtaposed redox groups capable of facilitating intramolecular electron transfer and begins to clarify in a simplified and malleable system the natural engineering of flavoproteins.     

Long-term progression in chronic manganism: ten years of follow-up

We studied the long-term clinical course of five patients with chronic manganese intoxication. The mean scores of the King's College Hospital Rating Scale for Parkinson's disease increased from 15.0 +/- 4.2 in 1987 to 28.3 +/- 6.70 in 1991 and then to 38.1 +/- 12.9 in 1995. The deterioration was most prominent in gait, rigidity, speed of foot tapping, and writing. Tissue concentrations of manganese in blood, urine, scalp hair, and pubic hair returned to normal. Follow-up MRIs did not show paramagnetic high-signal intensity on T1-weighted images. The data indicate that clinical progression in patients with manganese parkinsonism continues even 10 years after cessation of exposure.     

Exit of the pre-TCR from the ER/cis-Golgi is necessary for signaling differentiation, proliferation, and allelic exclusion in immature thymocytes

A major issue is whether surface expression of the pre-TCR is necessary for signaling the development of immature thymocytes. To address this question, we generated transgenic mice expressing a TCRbeta chain that had a strong endoplasmic reticulum (ER) retrieval signal (TCRbetaER) and that was expressed intracellularly but failed to reach the cell surface. In TCRbetaER transgenic mice, there was a failure of allelic exclusion. Also, the transgene failed to rescue the developmental defects observed in TCRbeta-null mice. In contrast, TCRbeta transgenes with a mutant ER retrieval sequence or lacking this sequence signaled efficient allelic exclusion and suppressed the TCRbeta-/- defect. These data show that exit of the pre-TCR from the ER/cis-Golgi is required for progression through the double-negative thymocyte checkpoint.