Flipping Lipids: Is the Third Time the Charm?

Certain membrane-spanning proteins expel hydrophobic molecules such as lipids and drugs from cells, but just how they accomplish this has been unclear. As [Davidson and Chen][1] describe in their Perspective, two new studies ([ Dong et al .][2], and [ Reyes et al .][3]) explain how a transporter protein called MsbA expends energy and changes its organization to flip a molecule from one side of the membrane to the other. [1]: http://www.sciencemag.org/cgi/content/full/308/5724/963 [2]: http://www.sciencemag.org/cgi/content/short/308/5724/1023 [3]: http://www.sciencemag.org/cgi/content/short/308/5724/1028