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Clathrin-dependent protein traffic


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Clathrin-dependent protein traffic

Clathrin-dependent protein traffic

Transport vesicles are classified according to the components of the protein coat thatsurrounds them during their genesis and early life. One of the most common and probablybest-characterized classes of coated vesicles are Clathrin -coated vesicles (CCVs)that cotain three protein layers. CCVs are so-called because the main component of thecoat is Clathrin, a complex that forms a polymeric mechanical scaffold on thevesicle surface. The inner, membrane layer with its embedded cargo is linked to the outerClathrin layer by a middle layer that consists of various clathrin-adaptormolecules and other proteins that have accessory/regulatory roles in CCV assembly.Classical key components of the absolute majority of the cargos in Clathrin-dependentendocytosis are Adaptor-related protein complex 2 ( AP complex 2 ) [1], [2], [3].

After the Clathrin lattice is formed, dynamins (e.g., Dynamin-2 ),endophilins (e.g., Endophilin B1 ), epsins and amphiphysins (e.g., BIN1 )are involved in membrane invagination and Clathrin rearrangements. The plus-endmotor Myosin I pulls the Dynamin-2 ring in the direction of the cellsurface, while the minus-end motor Myosin VI pulls the coated bud into thecytosol. The resulting strain could then sever the constricted stalk beneath the dynaminring [4].

Next phase is a fusion of coated-pit-derived primary endocytic vesicles with sortingendosomes. It is regulated by member RAS oncogene family Rab-5A, Early endosomeantigen 1 ( EEA1 ) [5], [6], [7] andSoluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNARE) [7], [8].

The maturation of sorting endosomes to late endosomes is realized with participationmember RAS oncogene family Rab7 via unknown mechanism [9], [10].

Late endosomes fusion to each other or to lysosomes via SNARE-mediated mechanism[11], [12], [8].

In addition, Rab7 is directly involved in the aggregation and fusion of lateendocytic structures/lysosomes [11], [13].

Subsequently, cargo is delivered to the Golgi from late endosomes with participationof RAS oncogene family Rab-9 [10], [14], [15].In addition, proteins from endoplasmic reticulum may be translocated to the Golgi in Coatprotein complex-II ( COPII )-dependent manner [16].

Modified in endoplasmic reticulum and/or Golgi, the cargo may be delivered from theGolgi back to the cell surface, possibly with participation of Rab8/Optineurin/ Myosin VI pathway [7], [17], [18] and/or coat protein complex termed Coatomer [19], [7], [20].

Moreover, cargo may be delivered to the cell surface via a short pathway fromendosomes via different recycling endosomes [7]. The latter is realizedmainly via Rab-4 and/or Rab-11A -dependent mechanisms [10],[21], [22].

It is shown, that recycling endosomes to the Golgi may be realized via different SNAREcomplexes [23], [7], [8].