West nile virus core protein: Tetramer structure and ribbon formation

We have determined the crystal structure of the core (C) protein from the Kunjin subtype of West Nile virus (WNV), closely related to the NY99 strain of WNV, currently a major health threat in the U.S. WNV is a member of the Flaviviridae family of enveloped RNA viruses that contains many important human pathogens. The C protein is associated with the RNA genome and forms the internal core which is surrounded by the envelope in the virion. The C protein structure contains four a. helices and forms dimers that are organized into tetramers. The tetramers form extended filamentous ribbons resembling the stacked alpha helices seen in HEAT protein structures.

Phosphatidylinositol 3-kinase C2 alpha is essential for ATP-dependent priming of neurosecretory granule exocytosis

Neurotransmitter release and hormonal secretion are highly regulated processes culminating in the calcium-dependent fusion of secretory vesicles with the plasma membrane. Here, we have identified a role for phosphatidylinositol 3-kinase C2 alpha (PI3K-C2 alpha) and its main catalytic product, PtdIns3P, in regulated exocytosis. In neuroendocrine cells, PI3K-C2 alpha is present on a subpopulation of mature secretory granules. Impairment of PI3K-C2 alpha function specifically inhibits the ATP-dependent priming phase of exocytosis. Overexpression of wild-type PI3K-C2 alpha enhanced secretion, whereas transfection of PC12 cells with a catalytically inactive PI3K-C2 alpha mutant or a 2xFYVE domain sequestering PtdIns3P abolished secretion. Based on these results, we propose that production of PtdIns3P by PI3K-C2 alpha is required for acquisition of fusion competence in neurosecretion.