assembles with membrane proteins
Syntaxin and SNAP 25 (Oyler et al. 1989; Bennett et al. 1992) and form a
ternary complex (Hanson et al. 1997). These proteins are the receptors for NSF
(N-ethylmaleimide-sensitive factor) and SNAPs (Soluble NSF attachment proteins)
and so-called SNAREs (SNAP receptors) (Söllner et al.
1993a, 1993b). These
SNARE proteins located at vesicles (v-SNARE) interacts with proteins at the
targeted membrane (t-SNARE) and help in fusion (Söllner et al. 1993a; Rothman and Warren,
1994). SNAREs that are aligned parallel to their transmembrane anchors during
docking (Otto et al. 1997), connects two membranes thereby zippering of v-SNARE
and t-SNARE (Hanson et al. 1997). The ATPase activity of NSF dissociates the
ternary SNARE complex (Söllner et al. 1993a; Hayashi et al.
1995). This leads to the conformational change of associated proteins and
induce fusion of secretory vesicle to the target membrane (Hanson et al. 1997).
This activity of NSF could be to dock new secretory vesicles thereby recruiting
new SNARE complexes (Hanson et al. 1997).
The importance of exocyst in cellular processes
is inevitable as it plays key role in exocytosis thereby mediating SNARE
mediated membrane fusion (He and Guo, 2009). The exocyst complex acts as a
signal receiver for various signaling pathways, help tether vesicles at the
receptor membrane and mediate fusion by inducing formation of SNARE assembly (He
and Guo, 2009; Žárský et al. 2013).
Various experiments have been done to prove its efficacy for growth, migration,
repair and defense by increasing or decreasing proteins, breaking the
association among the subunits and its associated proteins that are necessary
in this process (Novick et al. 1980; Hala et al. 2002; He et al. 2007; Zhang et
al. 2008). The exocyst mutants show secretion defects and intracellular
accumulation of the secretory vesicles (Novick et al. 1980; Guo et al. 1999; Zhang
et al. 2005, He et al. 2007; Zhang et al. 2008; Heider and Munson, 2012). The
mutation in exocyst subunit exo70 shows defects in secretion of secretory
vesicles (He et al. 2007) that transport endoglucanase Bg12 required for cell
membrane expansion and cell wall remodeling (He and Guo, 2009). Impairing the
connection of sec 3 and exo 70 with PI (4,5) P2 halts the fusion
process leading to cell death (He et al. 2007; Zhang et al. 2008). As exocyst
mediates the SNARE assembly, their mutants failed to form SNARE complex (Grote
et al. 2000).