The transport of cholesterol from NPC2 to NPC1 is essential for the maintenance of cholesterol homeostasis in late endosomes. On the basis of a rigid docking model of the crystal structures of the N-terminal cholesterol binding domain of NPC1(NTD) and the soluble NPC2 protein, models of the NPC1(NTD)-NPC2-cholesterol complexes at the beginning and the end of the transport as well as the unligated NPC1(NTD)-NPC2 complex were studied using 86 ns MD simulations. Significant differences in the cholesterol binding mode and the overall structure of the two proteins compared to the crystal structures of the cholesterol binding separate units were obtained. Relevant residues for the binding are identified using MM/GBSA calculations and the influence of the mutations analyzed by modeling them in silico, rationalizing the results of previous mutagenesis experiments. From the calculated energies and the NEB (nudged elastic band) evaluation of the cholesterol transfer mechanism, an atomistic model is proposed of the transfer of cholesterol from NPC2 to NPC1(NTD) through the formation of an intermediate NPC1(NTD)-NPC2 complex.

Full details of the previously reported total synthesis of streptonigrin (1) are presented. The successful synthetic strategy outlined in Scheme I involves use of an imino Diels-Alder cycloaddition for construction of the pyridine C ring of 1 and a modified Friedlander synthesis for annulation of the AB quinoline quinone ring system.

aqueous acetone was sealed in a Carius combustion tube and heated to the specified temperature for the desired amount of time. The tube was then cooled, the acetone removed with a stream of N2, and the resulting solution taken up in 25 mL of CH2C12. This was washed with 5% NaHC03 (2 X 30 mL) and water (30 mL), dried over Na2S04, and evaporated to dryness. The resulting products were then subjected to HPLC analysis.B. Benzene Solution. A mixture of ca. 100 mg of the compound and 10 mg of p-toluenesulfonic acid monohydrate in 25 mL of dry C6H6 was heated to reflux for 2 days. The reaction mixture was cooled and diluted with 20 mL of Et^O, washed with 5% NaHC03 (2 X 20 mL) and water (20 mL), dried over Na2S04, and evaporated to dryness. The resulting product was then subjected to HPLC analysis.

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