{'fraction_non_alphanumeric': 0.027061855670103094, 'fraction_numerical': 0.006013745704467354, 'mean_word_length': 5.673352435530086, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
C-terminal domain of mammalian complexin-1 localizes to highly curved membranes

Significance The central nervous system utilizes Ca2+-triggered synaptic vesicle fusion mediated by SNAREs and other synaptic proteins for neurotransmitter release into the synaptic cleft. Complexin, a small cytosolic protein, plays a dual role in regulating spontaneous minirelease and in activating Ca2+-triggered fusion, but the molecular mechanisms are still unclear. Here we found that the C-terminal domain of mammalian complexin interacts with membranes in a curvature-dependent fashion similar to other curvature-sensing proteins, such as α-synuclein. Together with a previous study of worm complexin, this finding suggests that curvature-sensing of the C-terminal domain is evolutionarily conserved. Moreover, localization to the highly curved membrane of synaptic vesicles is important for regulating spontaneous release by complexin. In presynaptic nerve terminals, complexin regulates spontaneous “mini” neurotransmitter release and activates Ca2+-triggered synchronized neurotransmitter release. We studied the role of the C-terminal domain of mammalian complexin in these processes using single-particle optical imaging and electrophysiology. The C-terminal domain is important for regulating spontaneous release in neuronal cultures and suppressing Ca2+-independent fusion in vitro, but it is not essential for evoked release in neuronal cultures and in vitro. This domain interacts with membranes in a curvature-dependent fashion similar to a previous study with worm complexin [Snead D, Wragg RT, Dittman JS, Eliezer D (2014) Membrane curvature sensing by the C-terminal domain of complexin. Nat Commun 5:4955]. The curvature-sensing value of the C-terminal domain is comparable to that of α-synuclein. Upon replacement of the C-terminal domain with membrane-localizing elements, preferential localization to the synaptic vesicle membrane, but not to the plasma membrane, results in suppression of spontaneous release in neurons. Membrane localization had no measurable effect on evoked postsynaptic currents of AMPA-type glutamate receptors, but mislocalization to the plasma membrane increases both the variability and the mean of the synchronous decay time constant of NMDA-type glutamate receptor evoked postsynaptic currents.