GRASP65 superhelix, topview [7]
Golgi reassembly-stacking protein of 65 kDa (GRASP65) also known as Golgi reassembly-stacking protein 1 (GORASP1) is a protein that in humans is encoded by the GORASP1 gene. [5]
Golgi reassembly-stacking protein of 65 kDa (GRASP65) also known as Golgi reassembly-stacking protein 1 (GORASP1) is a protein that in humans is encoded by the GORASP1 gene. [5]
The Golgi complex plays a key role in the sorting and modification of proteins exported from the endoplasmic reticulum. The GRASP65 protein is a peripheral membrane protein anchored to the lipid bilayer through myristoylation of a glycine residue near the protein's amino terminus. [7] It is involved in establishing the stacked structure of the Golgi apparatus and linking the stacks into larger ribbons in vertebrate cells. [7] It is a caspase-3 substrate, and cleavage of this encoded protein contributes to Golgi fragmentation in apoptosis. [8] [9] GRASP65 can form a complex with the Golgi matrix protein GM130, and this complex binds to the vesicle docking protein p115. [7] [lower-alpha 1] Several alternatively spliced transcript variants of this gene have been identified, but their full-length natures have not been determined. [5]
GRASP65 contains two PDZ domains in the amino-terminal GRASP domain (amino acid residues 2–210), that comprises approximately half of the protein. The GRASP region interacts with the Golgi matrix protein GM130 as well as an intrinsically disordered region in the C-terminus. [7] [10]
GORASP1 has been shown to interact with TGF alpha, [11] TMED2 [11] and GOLGA2. [11] [12] [13]
The Golgi apparatus, also known as the Golgi complex, Golgi body, or simply the Golgi, is an organelle found in most eukaryotic cells. Part of the endomembrane system in the cytoplasm, it packages proteins into membrane-bound vesicles inside the cell before the vesicles are sent to their destination. It resides at the intersection of the secretory, lysosomal, and endocytic pathways. It is of particular importance in processing proteins for secretion, containing a set of glycosylation enzymes that attach various sugar monomers to proteins as the proteins move through the apparatus.
A cisterna are all of the membrane-bound sacs that could be found in both the Golgi apparatus and in the Endoplasmic Reticulum. Cisterna are an integral part of the packaging and modification processes of proteins occurring in the Golgi. It is the flattened sac on the branch of the Endoplasmic Reticulum and the curved sac on the branch of the Golgi apparatus. The proteins begin on the cis side of the Golgi and exit on the trans side. Throughout their journey in the cisterna, the proteins are packaged and are modified for transport throughout the cell. The number of cisterna in the Golgi stack is dependent on the organism and cell type. The structure, composition, and function of each of the cisternae may be different inside the Golgi stack. These different variations of Golgi cisternae are categorized into 3 groups; cis golgi network, medial, and trans Golgi network. The cis Golgi network is the first step in the cisternal structure of a protein being packaged, while the trans Golgi network is the last step in the cisternal structure when the vesicle is being transferred to either the lysosome, the cell surface or the secretory vesicle. The cisternae are shaped by the cytoskeleton of the cell through a lipid bilayer. Post-translational modifications such as glycosylation, phosphorylation and cleavage occur in the Golgi and as proteins travel through it, they go through the cisternae, which allows functional ion channels to be created due to these modifications. Each class of cisternae contains various enzymes used in protein modifications. These enzymes help the Golgi in glycosylation and phosphorylation of proteins, as well as mediate signal modifications to direct proteins to their final destination. Defects in the cisternal enzymes can cause congenital defects including some forms of muscular dystrophy, cystic fibrosis, cancer, and diabetes.
Endosomes are a collection of intracellular sorting organelles in eukaryotic cells. They are parts of endocytic membrane transport pathway originating from the trans Golgi network. Molecules or ligands internalized from the plasma membrane can follow this pathway all the way to lysosomes for degradation or can be recycled back to the cell membrane in the endocytic cycle. Molecules are also transported to endosomes from the trans Golgi network and either continue to lysosomes or recycle back to the Golgi apparatus.
Golgin subfamily A member 2 is a protein that in humans is encoded by the GOLGA2 gene.
General vesicular transport factor p115 is a protein that in humans is encoded by the USO1 gene.
Ras-related protein Rab-1A is a protein that in humans is encoded by the RAB1A gene.
Syntaxin-6 is a protein that in humans is encoded by the STX6 gene.
Syntaxin-5 is a protein that in humans is encoded by the STX5 gene.
Synaptobrevin homolog YKT6 is a protein that in humans is encoded by the YKT6 gene.
Golgin subfamily A member 3 is a protein that in humans is encoded by the GOLGA3 gene.
NSFL1 cofactor p47 is a protein that in humans is encoded by the NSFL1C gene.
Golgi SNAP receptor complex member 1 is a protein that in humans is encoded by the GOSR1 gene.
Golgi reassembly-stacking protein of 55 kDa (GRASP55) also known as golgi reassembly-stacking protein 2 (GORASP2) is a protein that in humans is encoded by the GORASP2 gene. It was identified by its homology with GRASP65 and the protein's amino acid sequence was determined by analysis of a molecular clone of its complementary DNA. The first (N-terminus) 212 amino acid residues of GRASP55 are highly homologous to those of GRASP65, but the remainder of the 454 amino acid residues are highly diverged from GRASP65. The conserved region is known as the GRASP domain, and it is conserved among GRASPs of a wide variety of eukaryotes, but not plants. The C-terminus portion of the molecule is called the SPR domain. GRASP55 is more closely related to homologues in other species, suggesting that GRASP55 is ancestral to GRASP65. GRASP55 is found associated with the medial and trans cisternae of the Golgi apparatus.
BET1-like protein is a protein that in humans is encoded by the BET1L gene.
Conserved oligomeric Golgi complex subunit 3 is a protein that in humans is encoded by the COG3 gene.
Golgin subfamily A member 5 is a protein that in humans is encoded by the GOLGA5 gene.
Golgi SNAP receptor complex member 2 is a protein that in humans is encoded by the GOSR2 gene.
Transmembrane emp24 domain-containing protein 2 is a protein that in humans is encoded by the TMED2 gene.
Giantin or Golgin subfamily B member 1 is a protein that in humans is encoded by the GOLGB1 gene. Giantin is located at the cis-medial rims of the Golgi apparatus and is part of the Golgi matrix that is responsible for membrane trafficking in secretory pathway of proteins. This function is key for proper localisation of proteins at the plasma membrane and outside the cell which is important for cell function that is dependent on for example receptors and the extracellular matrix function. Recent animal model knockout studies of GOLGB1 in mice, rat, and zebrafish have shown that phenotypes are different between species ranging from mild to severe craniofacial defects in the rodent models to just minor size defects in zebrafish. However, in adult zebrafish a tumoral calcinosis-like phenotype was observed, and in humans such phenotype has been linked to defective glycosyltransferase function.
The Golgi matrix is a collection of proteins involved in the structure and function of the Golgi apparatus. The matrix was first isolated in 1994 as an amorphous collection of 12 proteins that remained associated together in the presence of detergent and 150 mM NaCl. Treatment with a protease enzyme removed the matrix, which confirmed the importance of proteins for the matrix structure. Modern freeze etch electron microscopy (EM) clearly shows a mesh connecting Golgi cisternae and associated vesicles. Further support for the existence of a matrix comes from EM images showing that ribosomes are excluded from regions between and near Golgi cisternae.
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