Metalloids: essential, beneficial or toxic? Major intrinsic proteins sort it out

Major intrinsic proteins (MIPs) are a family of selective membrane channels comprising water-channelling aquaporins and glycerol-channelling aquaglyceroporins. Recently, several MIPs within all domains of life were shown to facilitate the diffusion of reduced and non-charged species of the metalloids silicon, boron, arsenic and antimony. Metalloids encompass a group of biologically important elements ranging from the essential to the highly toxic. Consequently, all organisms require efficient membrane transport systems to control the exchange of metalloids with the environment. Recent genetic evidence has demonstrated a crucial role for specific MIPs in metalloid homeostasis. We propose that specific MIPs represent an ancient and indispensable transport mechanism for metalloids, which suggests that they could be potential pharmacological targets.