Structural and Functional Deficits in a Neuronal Calcium Sensor-1 Mutant Identified in a Case of Autistic Spectrum Disorder

Neuronal calcium sensor-1 (NCS-1) is a Ca2+ sensor protein that has been implicated in the regulation of various aspects of neuronal development and neurotransmission. It exerts its effects through interactions with a range of target proteins one of which is interleukin receptor accessory protein like-1 (IL1RAPL1) protein. Mutations in IL1RAPL1 have recently been associated with autism spectrum disorders and a missense mutation (R102Q) on NCS-1 has been found in one individual with autism. We have examined the effect of this mutation on the structure and function of NCS-1. From use of NMR spectroscopy, it appeared that the R102Q affected the structure of the protein particularly with an increase in the extent of conformational exchange in the C-terminus of the protein. Despite this change NCS-1(R102Q) did not show changes in its affinity for Ca2+ or binding to IL1RAPL1 and its intracellular localisation was unaffected. Assessment of NCS-1 dynamics indicated that it could rapidly cycle between cytosolic and membrane pools and that the cycling onto the plasma membrane was specifically changed in NCS-1(R102Q) with the loss of a Ca2+ -dependent component. From these data we speculate that impairment of the normal cycling of NCS-1 by the R102Q mutation could have subtle effects on neuronal signalling and physiology in the developing and adult brain

Neuronal calcium sensor-1 potentiates glucose-dependent exocytosis in pancreatic β cells through activation of phosphatidylinositol 4-kinase β

Cytosolic free Ca(2+) plays an important role in the molecular mechanisms leading to regulated insulin secretion by the pancreatic β cell. A number of Ca(2+)-binding proteins have been implicated in this process. Here, we define the role of the Ca(2+)-binding protein neuronal Ca(2+) sensor-1 (NCS-1) in insulin secretion. In pancreatic β cells, NCS-1 increases exocytosis by promoting the priming of secretory granules for release and increasing the number of granules residing in the readily releasable pool. The effect of NCS-1 on exocytosis is mediated through an increase in phosphatidylinositol (PI) 4-kinase β activity and the generation of phosphoinositides, specifically PI 4-phosphate and PI 4,5-bisphosphate. In turn, PI 4,5-bisphosphate controls exocytosis through the Ca(2+)-dependent activator protein for secretion present in β cells. Our results provide evidence for an essential role of phosphoinositide synthesis in the regulation of glucose-induced insulin secretion by the pancreatic β cell. We also demonstrate that NCS-1 and its downstream target, PI 4-kinase β, are critical players in this process by virtue of their capacity to regulate the release competence of the secretory granules