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].