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Figure 1


Fig. 1. Routes for non-conventional protein export. (A) Transporter channels. Cytoplasmic proteins can be exported through transporter-protein channels and then captured by cell-surface counter receptors. As an example, FGF2 is shown being exported through the ABC transporter and then captured by a heparin sulphate proteoglycan. (B) Protein-release complex. Other cytoplasmic proteins, such as epimorphin (or FGF1, not shown), associate with a protein-release complex that is composed of S100A13 and synaptotagmin 1 that then binds to annexin 2. The epimorphin protein-release complex is localized to, and flipped through, the cytoplasmic membrane in response to Ca2+ and phosphatidylserine. Released epimorphin then binds to {alpha}v-integrin, resulting in activation of morphogenic signaling cascades. (C) Flippase activity. An alternate route of export results from cytoplasmic proteins binding to transporter proteins that have intrinsic flippase activity when stimulated by phosphatidylserine. (D,E) Exocytosis and membrane blebbing. Additional mechanisms of non-conventional export include exocytosis (D) and membrane blebbing (E). Cytoplasmic and/or nuclear proteins such as Ku are released by exocytosis of exosomes, but cytoplasmic proteins can also be exported in vesicles formed by membrane blebbing.





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