Camera Iris Mechanism Saves Bacteria

Bacteria experience massive pressures against their membranes when they're suddenly exposed to fresh water, but they survive because they possess pressure-relieving protein floodgates in the form of ion channels. Now, two independent research teams propose that one such molecular safety valve works like a camera's iris.

Structural data for the closed form of MscS, a bacterial ion channel that opens in response to increases in membrane tension, already exist. However, trapping MscS in its open form has proven to be a challenge. In one study, led by Eduardo Perozo of the University of Chicago, researchers used cone-shaped lipids to alter the pressure on membrane-embedded MscS and open it (Science 2008, 321, 1210). They characterized the channel with electron paramagnetic resonance spectroscopy.

Meanwhile, James H. Naismith of the University of St. Andrews and Ian R. Booth of the University of Aberdeen, both in Scotland, led a team that crystallized a mutant MscS that is stuck in the open state and determined its X-ray structure (Science 2008, 321, 1179). Both teams suggest that the irislike motion removes a hydrophobic seal from the channel pore, thereby allowing water and ions through.