Biochemical pay dirt

Both halves of a protein, previously thought to operate with one half inactive, are required to produce ‘earth odour’, according to a paper in the November issue of Nature Chemical Biology. Geosmin – the chemical that is responsible for the smell of freshly ploughed soil – is produced by a number of micro-organisms. Although the chemical structure of geosmin has been known since 1965, the way it is made by these organisms has been difficult to decipher. Because geosmin causes an undesirable musty smell in water, wine and food products, understanding the biosynthesis of this earthy odour, beyond its chemical interest, may help in efforts to prevent musty food and drink.

David E. Cane and colleagues have now determined important details in the biosynthesis of geosmin. They did this by altering specific amino acids in the enzyme responsible for producing geosmin and chemically characterizing the enzymatic products of these ‘mutant’ enzymes. the authors demonstrated that one half of the protein catalyzes the formation of an intermediate chemical and then the other half of the protein turns this intermediate into geosmin.