The active zone is the presynaptic region in the nerve terminals that mediates neurotransmitter release and is composed a dense collection of proteins called the cytomatrix at the active zone (CAZ). The CAZ proteins are thought to mediate synapse formation and regulate neurotransmitter release [, ].This entry represents the ELKS family, which are thought to be involved in the organisation of CAZ. Vertebrate ELKS proteins are produced by two genes, ERC1 and ERC2. Caenorhabditis elegans expresses a homologue of ELKS that acts downstream of syd2/liprin-alpha during active zone assembly []. Drosophila melanogaster expresses a related protein termed bruchpilot (brp) that consists of a conserved N terminus and a C-terminal half with no homologous sequences in vertebrates. Brp is required for structural integrity and function of synaptic active zones []. Vertebrate ELKS proteins are enriched at presynaptic active zones []and support Ca2+ influx at nerve terminals of inhibitory hippocampal neurons []. They have a C-terminal PDZ-binding motif that binds directly to RIM (a small G protein Rab-3A effector). These proteins also contain four coiled-coil domains [].
The Rab11 GTPase regulates recycling of internalized plasma membrane receptors and is essential for completion of cytokinesis. A family of Rab11 interacting proteins (FIPs) that conserve a C-terminal Rab-binding domain (RBD) selectively recognise the active form of Rab11. FIPs are diverse in sequence length and composition toward their N-termini, presumably a feature that underpins their specific roles in Rab11-mediated vesicle trafficking. They have been divided into three subfamilies (classe I, II, and III)on the basis of domain architecture. Class I FIPs comprises a subfamily of three proteins (Rip11/pp75/FIP5, Rab-coupling protein (RCP), and FIP2) that possess an N-terminal C2 domain, localize to recycling endosomes, and regulate plasma membrane recycling. The class II subfamily consists of two proteins (FIP3/eferin/arfophilin and FIP4) with tandem EF hands and a proline-rich region. Class II FIPs localize to recycling endosomes, the trans-Golgi network, and have been implicated in the regulation of membrane trafficking during cytokinesis. The class III subfamily consists of a single protein, FIP1, which does not contain obvious homology domains or motifs other than the FIP-RBD [, , , ].The FIP-RBD domain is also found in Rab6-interacting protein Erc1/Elks. Erc1 is the regulatory subunit of the IKK complex and probably recruits IkappaBalpha/NFKBIA to the complex []. It may be involved in the organisation of the cytomatrix at the nerve terminals active zone (CAZ) which regulates neurotransmitter release. It may also be involved in vesicle trafficking at the CAZ, as well as in Rab-6 regulated endosomes to Golgi transport [].The FIB-RBD domain consists of an N-terminal long α-helix, followed by a 90 degrees bend at a conserved proline residue, a 3(10) helix and a C-terminal short β-strand, adopting an "L"shape. The long α-helix forms a parallel coiled-coil homodimer that symmetrically interacts with two Rab11 molecules on both sides, forming a quaternary Rab11-(FIP)2-Rab11 complex. The Rab11-interacting region of FIP-RBD is confined to the C-terminal 24 amino acids, which cover the C-terminal half of the long α-helix and the short β-strand [, , , ]. This entry represents the FIP-RBD C-terminal domain.
The Rab11 GTPase regulates recycling of internalized plasma membrane receptors and is essential for completion of cytokinesis. A family of Rab11 interacting proteins (FIPs) that conserve a C-terminal Rab-binding domain (RBD) selectively recognise the active form of Rab11. FIPs are diverse in sequence length and composition toward their N-termini, presumably a feature that underpins their specific roles in Rab11-mediated vesicle trafficking. They have been divided into three subfamilies (classe I, II, and III)on the basis of domain architecture. Class I FIPs comprises a subfamily of three proteins (Rip11/pp75/FIP5, Rab-coupling protein (RCP), and FIP2) that possess an N-terminal C2 domain, localize to recycling endosomes, and regulate plasma membrane recycling. The class II subfamily consists of two proteins (FIP3/eferin/arfophilin and FIP4) with tandem EF hands and a proline-rich region. Class II FIPs localize to recycling endosomes, the trans-Golgi network, and have been implicated in the regulation of membrane trafficking during cytokinesis. The class III subfamily consists of a single protein, FIP1, which does not contain obvious homology domains or motifs other than the FIP-RBD [, , , ].The FIP-RBD domain is also found in Rab6-interacting protein Erc1/Elks. Erc1 is the regulatory subunit of the IKK complex and probably recruits IkappaBalpha/NFKBIA to the complex []. It may be involved in the organisation of the cytomatrix at the nerve terminals active zone (CAZ) which regulates neurotransmitter release. It may also be involved in vesicle trafficking at the CAZ, as well as in Rab-6 regulated endosomes to Golgi transport [].The FIB-RBD domain consists of an N-terminal long α-helix, followed by a 90 degrees bend at a conserved proline residue, a 3(10) helix and a C-terminal short β-strand, adopting an "L"shape. The long α-helix forms a parallel coiled-coil homodimer that symmetrically interacts with two Rab11 molecules on both sides, forming a quaternary Rab11-(FIP)2-Rab11 complex. The Rab11-interacting region of FIP-RBD is confined to the C-terminal 24 amino acids, which cover the C-terminal half of the long α-helix and the short β-strand [, , , ]. This entry represents the FIP-RBD C-terminal domain.
