, 2011). Binding of the RIM zinc-finger to the Munc13 C2A domain disrupts the homodimers, thereby activating Munc13. As a result, RIM-deficient synapses exhibit a severe impairment in vesicle priming that can be click here rescued not only by the N-terminal RIM fragment, but also by expression of mutant Munc13 that is constitutively

monomeric, illustrating that the function of RIMs in priming consists of activating Munc13 (Deng et al., 2011). In addition to the regulation of the Munc13 MUN domain by RIMs, the MUN domain is controlled by the central signaling domains of Munc13 that comprise a calmodulin-binding sequence and the C1 and C2B domains (Figure 2) and that perform essential functions in regulating release (Rhee et al., 2002; Junge et al., 2004; Shin et al., 2010; see discussion below). It is unknown, however, whether the N-terminal sequences of bMunc13-2 and Munc13-3 have a regulatory role since they do not bind to RIMs, and no function has been observed yet for the conserved C2C domain of Munc13s. Addressing these questions may have general implications not only for synaptic exocytosis, I-BET151 research buy but also for other forms of exocytosis,

for example cytotoxic granule exocytosis in NK cells which requires Munc13-4 (Feldmann et al., 2003). α- and β-liprins are related proteins composed of an N-terminal half with a predicted coiled-coil domain, and three ADAMTS5 C-terminal SAM domains (Serra-Pagès et al., 1995). Two highly conserved sequence motifs in the N-terminal coiled-coil region are referred to as “liprin homology domains” LH1 and LH2 (Taru and Jin, 2011). The N-terminal half of α-liprins binds to itself to form homodimers (Taru and Jin, 2011), to the RIM

C2B domain (Schoch et al., 2002), to ELKS (Ko et al., 2003a and Dai et al., 2006), to mDiaphanous, a rho effector protein (Sakamoto et al., 2012), and to GIT1 (Ko et al., 2003b). The C-terminal SAM-domains, in turn, bind to β-liprins to form heterodimers (Serra-Pagès et al., 1995), to CASK (Olsen et al., 2005), and to LAR-type receptor phosphotyrosine phosphatases (PTPRF, PTPRD, and PTPRS; Serra-Pagès et al., 1995). Of these interactions, α-liprin binding to β-liprins, to receptor phosphotyrosine phosphatases, to ELKS, and to itself have been functionally validated (Kaufmann et al., 2002, Ackley et al., 2005, Dai et al., 2006, Taru and Jin, 2011 and Astigarraga et al., 2010). α-Liprins were first linked to presynaptic active zones when a loss-of-function mutation in C. elegans α-liprin was found to apparently increase the size of the active zone and to disrupt synaptic vesicle accumulation ( Zhen and Jin, 1999 and Dai et al., 2006), a finding that was confirmed in Drosophila ( Kaufmann et al., 2002). No studies on α-liprin function in vertebrate presynaptic terminals exist, but a rich body of work in C.