Cargo proteins/molecules

Table 2 is a compilation of 11 proteomic studies of exosomes released by various cells in culture, compared with the data of the complete study done on exosomes collected from urine. Note that of the 22 proteins found in at least 4 of the 11 studies, 20 were also found in urine exosomes. These findings suggest that these proteins are very likely involved in the biogenesis or sorting of molecules in the vesicles. Other proteins are not systematically found in the various studies and might reflect variation between cell types, such as differential expression of cargo proteins. 

Proteins similar to importins, referred to as ex-portins, are involved in export of many macromolecules from the nucleus. Cargo molecules for export carry nuclear export signals (NESs). Ran proteins are involved in this process also, and it is now established that the processes of import and export share a number of common feamres. 

Two examples are dynein and kinesin. These huge proteins latch onto vesicles—membrane-bound compartments—filled with certain molecules and transport this cargo to another region of the cell. The proteins walk along filaments inside the cell, using the energy-rich compound adenosine triphosphate (ATP) as fuel. 

Figure 4 Examples of mimics of ligands and receptors used to deliver cargo into cells. (a,b) Ligands such as folate can be linked to macromolecules (e.g., nucleic acids and proteins) and small molecules (e.g., drugs, radiochemicals, and fluorophores) to promote cellular uptake, (c) Peptides and small molecules linked to N-alkyl derivatives of 3p-cholesterylamine or 3p-dihydrocholesterylamine mimic cell-surface receptors by cycling rapidly between the plasma membrane and the intracellular endosomes. The synthetic Fc receptor shown in (c) enables treated mammalian cells to internalize human igG.

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