Distinct roles of the C 2}A and the C 2}B domain of the vesicular Ca 2+} sensor synaptotagmin 9 in endocrine {beta}-cells

Florence Grise , Nada Taib , Carole Monterrat , Valérie Lagrée , Jochen Lang (1)

1 Mol Cell Biol, JE2390

Synaptotagmins form a family of calcium-sensor proteins implicated in exocytosis and these vesicular transmembrane proteins are endowed with two cytosolic calcium-binding C 2} domains, C 2}A and C 2}B. Whereas the isoforms syt1 and 2 have been studied in detail, less is known on syt9, the calcium sensor of endocrine secretion such as insulin release from large dense core vesicles in pancreatic {beta}-cells. Using cell based assays to closely mimic physiological conditions, we observed SNARE-independent translocation of syt9C 2}AB to the plasma membrane at calcium levels corresponding to endocrine exocytosis and followed by internalisation to endosomes. The use of point mutants and truncations revealed that initial translocation required only the C 2}A domain, whereas the C 2}B domain ensured partial pre-binding of syt9C 2}AB to the membrane and post-stimulatory localisation to endosomes. In contrast to the known properties of neuronal and neuroendocrine syt1 or syt2, the C 2}B domain of syt9 did not undergo calcium-dependent membrane binding despite a high degree of structural homology as observed through molecular modelling. These studies demonstrate distinct intracellular properties of syt9 with different roles for each C 2} domain in endocrine cells.

Mots clés: Life Sciences

Florence Grise, Nada Taib, Carole Monterrat, Valérie Lagrée, Jochen Lang. Distinct roles of the C 2}A and the C 2}B domain of the vesicular Ca 2+} sensor synaptotagmin 9 in endocrine {beta}-cells. Biochemical Journal, 2007, 403 (3), pp.483-492. ⟨10.1042/BJ20061182⟩. ⟨hal-00478645⟩