Synaptotagmin-11 inhibits clathrin-mediated and bulk endocytosis

Precise and efficient endocytosis is essential for vesicle recycling during a sustained neurotransmission. The regulation of endocytosis has been extensively studied, but inhibitors have rarely been found. Here, we show that synaptotagmin-11 (Syt11), a non-Ca²⁺-binding Syt implicated in schizophrenia and Parkinson's disease, inhibits clathrin-mediated endocytosis (CME) and bulk endocytosis in dorsal root ganglion neurons. The frequency of both types of endocytic event increases in Syt11 knockdown neurons, while the sizes of endocytosed vesicles and the kinetics of individual bulk endocytotic events remain unaffected. Specifically, clathrin-coated pits and bulk endocytosis-like structures increase on the plasma membrane in Syt11-knockdown neurons. Structural-functional analysis reveals distinct domain requirements for Syt11 function in CME and bulk endocytosis. Importantly, Syt11 also inhibits endocytosis in hippocampal neurons, implying a general role of Syt11 in neurons. Taken together, we propose that Syt11 functions to ensure precision in vesicle retrieval, mainly by limiting the sites of membrane invagination at the early stage of endocytosis. Synopsis This study identifies Syt11 as an inhibitory regulator for neuronal endocytosis. Syt11 inhibits both clathrin-mediated and bulk endocytosis probably at the stage of membrane invagination. Syt11 inhibits clathrin-mediated endocytosis (CME) and bulk endocytosis in mammalian neurons. Syt11 limits the formation of clathrin-coated pits and and bulk endocytosis-like structures on the plasma membrane. Membrane localization and AP-2-binding ability of Syt11 are critical for CME. The Syt11 C2A domain is not necessary for CME while both C2 domains are required for bulk endocytosis. This study identifies Syt11 as an inhibitory regulator for neuronal endocytosis. Syt11 inhibits both clathrin-mediated and bulk endocytosis probably at the stage of membrane invagination.