Drosophila AD3 mutation of synaptotagmin impairs calcium-dependent self-oligomerization activity

Genetic analysis of a Drosophila synaptotagmin (Syt) I mutant (AD3) has revealed that Tyr-334 within the C2B domain is essential for efficient Ca2+-dependent neurotransmitter release. However, little is known as to why a missense mutation (Tyr-334-Asn) disrupts the function of the C2B domain at the molecular level. Here, we present evidence that a Tyr-312 to Asn substitution in mouse Syt II, which corresponds to the Drosophila AD3 mutation, completely impairs Ca2+-dependent self-oligomerization activity mediated by the C2B domain but allows partial interaction with wild-type proteins in a Ca2+-dependent manner. This observation is consistent with the fact that the AD3 allele is homozygous lethal but complements another mutant phenotype. We also showed that the Ca2+-dependent C2B self-oligomerization is inhibited by inositol 1,3,4,5-tetrakisphosphate, a potent inhibitor of neurotransmitter release. All of these findings strongly support the idea that self-oligomerization of Syt I or II is essential for neurotransmitter release in vivo. (C) 2000 Federation of European Biochemical Societies. Published by Elsevier Science B.V. All rights reserved.