Cellular chemistry down the tubes

Membrane Tube Network Formation. Click image to magnify.

Cells need to talk to each other in order to work together but their own internal communications systems are just as important. Now, a team from the Curie Institute have developed a system of giant bubble-like vesicles, minibeads, and molecular motors that mimic the transport of chemical species in and around the cell.

Membrane transport tubes were first discovered several years ago, but how they form and work is still a mystery to biologists. In an effort to provide a model system that could open up communication channels between scientists a team of CNRS biologists and physicists have produced a minimal system in the laboratory that emulates intracellular transport in molecular tubes.

Biologist Bruno Goud and physical chemist Patricia Bassereau have used natural cell constituents to build their cellular model. They used an in vitro version of the cell's microtubule-based support structure, which serve as tracks along which chemicals in the cell can be ferried to their target sites. Moreover, molecular motors - proteins called kinesins - drive these chemicals along the channels. Kinesins are composed of two chains, the ends of which can lock on to the energy biomolecule adenosine triphosphate (ATP).

	Intracellular Communication. Click image to magnify.

The team has made giant vesicles of more than 10-micrometers in diameter from a single lipid membrane. These structures resemble a membranous fluid-filled cell. 100-nanometer polystyrene beads are then coated with biotin, one end of which can lock on to the lipids in the vesicle wall while the other latches on to kinesin. The tiny bead on the vesicle's surface thus starts stretching the vesicle as one end pulls one way and the other end is pulled by kinesin in the opposite direction.

in vitro Membrane Tube Formation. Click image to magnify.

The result is that several very fine tubes are formed from the stretched vesicles just a few dozen nanometers in diameter. The individual tubules then begin to network together forming a complex microtubule-aligned system, as predicted. The researchers point out the similarities between this system and the endoplasmic reticulum or the Golgi apparatus within a living cell.

The team believes their work might have applications in cell transport studies, nanotechnology, and in studying the membrane proteins of cancer cells.

Proc. Natl. Acad. Sci. (USA), 2002, 99(8), 5394; http://www.pnas.org/cgi/content/full/99/8/5394.