A proper protein function requires correct protein transport to target sites in the cell. In general, proteins are synthesized in the endoplasmatic reticulum, transported to the Golgi and the trans-Golgi network (TGN) and transferred to the cell membrane via different post-Golgi transport intermediates such as vesicles (De Matteis and Luini, 2008; Griffiths and Simons, 1986).

There are different types of vesicles known in the cell:

Adaptor protein coated or adaptor protein-clathrin coated vesicles bud off the TGN and target to endosomes or the plasma membrane (Robinson, 2004; Rodriguez-Boulan et al., 2005).

Early endosomes are required for sorting of proteins and lipids that enter the cell through clathrin-mediated endocytosis (Maxfield and McGrar, 2004).

Recycling endosomes are involved in receptor transport to the plasma membrane (Brown et al., 2000).

Late endosomes mature from early andosomes by Rab protein conversion

Lysosomes are a site of protein degradation by acid hydrolases (Rink et al., 2005; Mullock et al., 1998; Tjelle et al., 1996).

Vacuoles arise either by auto-phagocytosis or through the fusion of vesicles and function in protein degradation or protein storage for degradation (Schworer et al., 1981; Klionsky and Ohsumi, 1999).

Certain target organelles, require a specific transport pathway. However, often these pathways are not very well described. Vesicle transport requires the cytoskeleton such as actin, myosin and microtubules and transport motors such as kinesin and dynein.