Lipids affect channel function
Many membrane channels, for proper function, require the presence of particular species of lipid in the surrounding membrane. In a recent paper in BMC Biology, Locke and Harris [1] provide an example of this: they showed that connexin channels are inactive in a membrane composed of just the zwitterionic lipid phosphatidylcholine (PC) but become active in the presence of the anionic lipid phosphatidylserine (PS) (for lipid structures see Figure 1). The full effect of PS is seen only when 60% or more of the lipid is PS. The effect is not structurally specific; other anionic lipids such as phosphatidic acid (PA) and phosphatidylinositol (PI) have the same effect as PS. Similar observations have been made with other channels. For example, the probability that the potassium channel KcsA is open is very low in bilayers of PC alone but increases with increasing anionic lipid content [2]; the functions of inward rectifying potassium channels are modulated by PIs [3]; and the presence of anionic lipid increases the rate of flux of small molecules through the mechanosensitive channel MscL [4].