biostudies-literatureLiang QNational Institutes of HealthNIGMS NIH HHS3370-3380https://www.ebi.ac.uk/biostudies/studies/S-EPMC9515229biostudies-literatureUnknown121(18)Complexin-1 is an essential protein for neuronal exocytosis that acts to depress spontaneous fusion events while enhancing evoked neurotransmitter release. In addition to binding soluble N-ethylmaleimide-sensitive factor attachment protein receptors, it is well established that complexin associates with membranes in a manner that depends upon membrane curvature. In the present work, we examine the membrane binding of complexin using electron paramagnetic resonance spectroscopy, fluorescence anisotropy, and total internal reflection fluorescence microscopy. The apparent membrane affinity of complexin is found to strongly depend upon the concentration of protein used in the binding assay, and this is a result of a limited number of binding sites for complexin on the membrane interface. AlthoBiophysical journalComplexin-1 and synaptotagmin-1 compete for binding sites on membranes containing PtdInsP₂.PMC9515229P01 GM072694Tamm LKCafiso DSKiessling VLiang QOfosuhene APLiang BKreutzberger AJBfalseComplexin-1 and synaptotagmin-1 compete for binding sites on membranes containing PtdInsP₂.Complexin-1 is an essential protein for neuronal exocytosis that acts to depress spontaneous fusion events while enhancing evoked neurotransmitter release. In addition to binding soluble N-ethylmaleimide-sensitive factor attachment protein receptors, it is well established that complexin associates with membranes in a manner that depends upon membrane curvature. In the present work, we examine the membrane binding of complexin using electron paramagnetic resonance spectroscopy, fluorescence anisotropy, and total internal reflection fluorescence microscopy. The apparent membrane affinity of complexin is found to strongly depend upon the concentration of protein used in the binding assay, and this is a result of a limited number of binding sites for complexin on the membrane interface. Altho2022-01-01T00:00:00Z2022 Sep2026-05-28T01:23:26.995Z2025-04-07T10:25:32.712ZS-EPMC95152293601649710.1016/j.bpj.2022.08.023