Endocytci adaptors are categorised into multimeric and monomeric adaptors proteins. The most studied endocytosis is clathrin- mediated pathway while the most abundant AP-2 is non-clathrin component of endocytic vesicles (Conner and Schmid, 2003). AP-2 is enriched membrane of plasma (Gaidarov et al., 1996; Collins et al. 2002; Rohde et al., 2002). Additionally, cargo-binding select diferent categories of plasma membrane to be internalised by binding to the signals in the cytoplasmic ends of the membrane (Ohno et al., 1995; Owen and Evans, 1998).
Short ubiquitin of bond to residues of lysine using covalent bonds in the trans-membrane receptors. Duncan et al (2006) and Hawryluk et al (2006) notes that there is sufficient evidence that indicates the need for short chains of ubiquitin in the internalisation of receptor is due to the inability of the single-ubiquitin to complete internalisation of receptors
According to Galan and Haguenauer-Tsapis, (1997) and Haglund (2003), Monoubiquitin are covalently bonded to lysine residues in trans-membrane receptors and can signal the internalization of cargo (; Haglund et al., 2003 ;).
Also, there are numerous Dx[F/W] motifs in the epsin 1 and epsin 2 for binding and domain binding of EPS15 homology (Benmerah et al., 1996; Chen et al., 1998; Maldonado-Baez et al., 2008).
Stonins lack in prokaryotes but are conserved from Caenorhabditis elegans to humans (Maritzen et al., 2010). The availability of Arrestins is crucial for carrying nutrients and passing signals to receptors (Ma and Pei, 2007; Lefkowitz and Shenoy, 2005). They control internalisation ad activation of trans-membrane G-protein with the assistance of GPCRSs receptors (Gourevitch).
According to Lohse et al. (1990), b-arrestins in the control of GPCRSS signalling by binding to phosphorylated GPCRSs and attenuating signalling. Additionally, b-arrestins facilitate the reception of endocytosis by associating with endocytic proteins (Laporte et al., 2000; Goodman et al., 1996).
According to Stamena et al. (2004) and Yu and Cai (2004), there is no homolog in yeast protein Sla 1 although it has been compared with CIN85 and intersecting (Stamenova et al., 2004; Yu and Cai, 2004). Kaksonen et al. (2003) and Warren et al. (2002), Sla 1 share characteristics with clathrin adaptors. It attaches to proteins of endocytic accessory.
Endocytic adaptors and disease
The coat component of GGA family of proteins has not been well examined. The Golgi-localised proteins act as monomeric adaptors for the trans-Golgi network. Mammals contain three genes while budding yeast contain only two.
The link between GGAs and AP-1 is not well known. They possess localised patterns but are not identical. The GGAs are more abundant in perinuclear membranes while AP-1 has peripheral distribution. It has been suggested that the two GGAs and AP-1 operate in sequential ways such that GGAs give more cag proteins to AP-1 on parallel pathways.
The function of GGA proteins in mammalian cells
The high GGA proteins lead changes in the Golgi (Takatsu et al., 2000; Boman et al., 2000; Poussu et al., 2000). Moderate levels of GGA protein excessive expression lead to localisation of coat proteins and cargo with not impact on the Golgi morphology.
GGAs contact with other proteins
GGA interact directly with proteins like coats and cargo. Boman et al. (2000) and Zhdankina et al. (2001) notes that GGA were previously known for their interaction with ARF proteins.
Pure GST-GGA proteins interact with GTP-bound ARF.
According to Boman et al. (2000) and Zhdankina et al. (2001), the part of GGA that interacts with ARF residues between 170 to 3330 which is the span of GTA domain. ARF3 mutation that does not connect with GGA1 take place occur in the switch I area (Kuai et al (2000). These mutants fail to interact with the GAT domain of GGA3 (Puertollano et al., 2001b).
Human GGA proteins have been shown to be ARF effectors. Zhang et al 91994) notes that the expression of the activating mutant of ARF leads to dramatic expansion of Golgi lumen (Zhang et al., 1994). Excessive expression of GGA1 stops expansion of the Golgi.
Research has indicated localisation of proteins at Golgi is caused by its communication with ARF(Poussu et al., 2000; DellAngelica et al., 2000; Hirst et al., 2000; ). Interaction of GAT with ARF is sufficient to initiate the construct of reporter (GFP) onto the Golgi. Additionally, mutations within the ARF-binding domain lead to the depletion of localisation of Golgi. (Puertollano et al., 2001b). Our findings reveal that proteins of GGA are recruited by ARF-GTP into the Golgi membrane by associating with GAT domain.
GGAs in virus assembly
The depletion of GGA2 and GGA3 enhances the release of viruses (Joshi et al., 2008). GGA on the other hand inhibits the release retroviruses. The HIV-1 particle poor production of particles caused by GGA is due to association with Gag membrane. Our findings revealed a coaction between ARF proteins and inhibition of mediated GGA overexpression.
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