Anhydrobiosis: the water replacement hypothesis

Abstract

Both the association of amphiphiles to form phospholipid bilayers and the folding of proteins that results in their tertiary structure are profoundly influenced by the low solubility of hydrocarbons in water (e.g. Tanford, 1978). These molecular arrangements, which are thought to be entropically driven, are lost when the water in which they are formed is removed. For instance, when a biological membrane is dehydrated, irreversible changes occur in its structural (Crowe and Crowe, 1982) and functional (Crowe, Crowe and Jackson, 1983) integrity. Similarly, many labile proteins lose their functional (reviewed in Carpenter, 1994) and probably structural (Prestrelski, Arakawa and Carpenter, 1993) integrity when they are desiccated. However, since the mid-1970s evidence has been accumulating that certain sugars may replace the water around polar residues in membrane phospholipids and proteins, maintaining their integrity in the absence of water. In this review we provide a current summary of what is known about the mechanism of these effects.