Communication between neurons involves presynaptic neurotransmitter release which can be evoked by action potentials or occur spontaneously as a result of stochastic vesicle fusion. The Ca2+-binding double C2 proteins Doc2a and -b were implicated in spontaneous and asynchronous evoked release, but the mechanism remains unclear. Here, we compared wildtype Doc2b with two Ca2+ binding site mutants named DN and 6A, previously classified as gain- and loss-of-function mutants. They carry the substitutions D218,220N or D163,218,220,303,357,359A respectively. We found that both mutants bound phospholipids at low Ca2+ concentrations and were membrane-associated in resting neurons, thus mimicking a Ca2+-activated state. Their overexpression in hippocampal primary cultured neurons had similar effects on spontaneous and evoked release, inducing high mEPSC frequencies and increased short-term depression. Together, these data suggest that the DN and 6A mutants both act as gain-of-function mutants at resting conditions.
Bourgeois-Jaarsma, Q., Verhage, M., & Groffen, A. J. (2019). Doc2b Ca2+ binding site mutants enhance synaptic release at rest at the expense of sustained synaptic strength. Scientific Reports, 9(1), 14408. . https://doi.org/10.1038/s41598-019-50684-1