The Exo70 protein is a subunit of the exocyst complex [1-7], first identified in yeast, it is evolutionarily conserved. It mediates the tethering of post-Golgi secretory vesicles to the plasma membrane and promotes the assembly of the SNARE complex for membrane fusion [1,2,3,4]. It also plays a role in cell polarisation, primary ciliogenesis, cytokinesis, pathogen invasion, tumourigenesis and metastasis [6]. It is a member of the the Complex Associated with Tethering Containing Helical Rods (CATCHRs) family which also includes Conserved Oligomeric Golgi complex (COG) and Golgi-Associated Retrograde Protein complex (GARP) and DSL1 complexes, all evolutionarily related and share structural features consisting of alpha-helical bundles at the C-terminus and coiled-coil region at the N-terminus [5,6]. Exo70 interacts with phospholipids and Rho3 GTPase [4,5,7]. This interaction mediates one of the three known functions of Rho3 in cell polarity: vesicle docking and fusion with the plasma membrane (the other two functions are regulation of actin polarity and transport of exocytic vesicle from the mother cell to the bud) [3]. This is the C-terminal domain of Exo70, which consists of alpha-helical bundles involved in binding the small GTPase Rho3 and it is important for localization to the plasma membrane as it directly interacts with phosphatidylinositol 4,5-biphosphate The interaction with phospholipids is essential for the membrane association of the exocyst complex [5,6,7].

1: The Exocyst is a multiprotein complex required for exocytosis in Saccharomyces cerevisiae. TerBush DR, Maurice T, Roth D, Novick P; EMBO J 1996;15:6483-6494. PMID:8978675

2: Subunit structure of the mammalian exocyst complex. Kee Y, Yoo JS, Hazuka CD, Peterson KE, Hsu SC, Scheller RH; Proc Natl Acad Sci U S A 1997;94:14438-14443. PMID:9405631

3: The Rho GTPase Rho3 has a direct role in exocytosis that is distinct from its role in actin polarity. Adamo JE, Rossi G, Brennwald P; Mol Biol Cell 1999;10:4121-4133. PMID:10588647

4: Rho3 of Saccharomyces cerevisiae, which regulates the actin cytoskeleton and exocytosis, is a GTPase which interacts with Myo2 and Exo70. Robinson NG, Guo L, Imai J, Toh-E A, Matsui Y, Tamanoi F; Mol Cell Biol 1999;19:3580-3587. PMID:10207081

5: Crystal Structure of the S.cerevisiae Exocyst Component Exo70p. Hamburger ZA, Hamburger AE, West AP Jr, Weis WI; J Mol Biol. 2005; [Epub ahead of print] PMID:16359701

6: Cryo-EM structure of the exocyst complex. Mei K, Li Y, Wang S, Shao G, Wang J, Ding Y, Luo G, Yue P, Liu JJ, Wang X, Dong MQ, Wang HW, Guo W; Nat Struct Mol Biol. 2018;25:139-146. PMID:29335562