Tunneling Through Cell Walls

Biological membranes are selectively permeable and regulate the exchange of material between cells and their surroundings. This exchange is largely controlled by protein channels that mediate transmembrane movement of ions and molecules. Synthetic analogs of these channels could be used for research and therapeutic purposes. Geng and colleagues demonstrated that, despite their structural simplicity, single-wall carbon nanotubes (CNTs) can be used as a scaffolding for channels—and they can function like their natural counterparts. To produce nanotubes of the right size for a transmembrane channel, the authors mixed lipids with longer nanotubes, then cut them to the right length for spanning the bilayer. The lipid coating allowed the CNTs to spontaneously incorporate into membranes of living cells. To test the functionality of these nanotube “CNT porins,” the team established that salts and water moved easily across the membrane through them. The end of the nanotube could also open and close much like biological ion channels, which may prove useful for applications where controlling membrane permeability is desired. Furthermore, the CNT porins could efficiently transport DNA across cell membranes, which opens the door for their use as gene delivery portals. There is a long way to go before the therapeutic value of CNT porins is established. For example, intravenously injected CNTs (which largely accumulate in the lung and liver) have not been ruled safe by regulatory authorities. But, it is easy to imagine that they may eventually prove essential for creating synthetic biomimetic cells and better biosensors, or even improve DNA sequencing by using nanopores for discerning different base pairs within DNA segments. J. Geng et al ., Stochastic transport through carbon nanotubes in lipid bilayers and live cell membranes. Nature 514 , 612–615 (2014). [[Full Text]][1] [1]: http://www.nature.com/nature/journal/v514/n7524/full/nature13817.html