In all living organisms, molecules are transformed into new chemical substances through processes which are catalysed by enzymes. Enzymes are proteins whose catalysing capacity enables chemical reactions which otherwise would not occur with sufficient speed or in a controlled way. The molecular evolution of enzymes is based on major or minor structural changes in a protein, which acquires new catalytic characteristics through the modification. The mutations in the genetic material which cause these structural changes have been regarded as random, but in certain cases it appears as if certain positions in a protein mutate more frequently than other positions in the protein. These specific positions are assumed to be particularly important to the biological functions of the protein.
Glutathione transferases are a family of enzymes which catalyse the detoxification of a broad spectrum of mutagens and carcinogens. Through major or minor structural variations, these enzymes have acquired new characteristics, thereby giving rise to more detoxification enzymes and a reinforced defence against toxic substances. A team of researchers led by Professor Bengt Mannervik has now shown that mutations in a single position in a glutathione transferase can dramatically alter the enzyme’s capacity to act selectively on various toxic substances. Through one type of mutation, the enzyme will become adapted to reactions in which the reactive group in the toxic substance is split off and replaced by glutathione, the body’s protective substance; through alternative mutations, the enzyme acquires the capacity to neutralise other reactive groups by linking them with glutathione.
“This discovery shows how the evolution of new enzyme functions may be quickly adapted to new needs. This is particularly significant for the defence against new toxins which may appear and threaten the survival of biological organisms,” says Bengt Mannervik.
This new study complements an earlier study by the research team, published in Science in January, which showed how a protein could be tailored to fulfil new functions through major changes to its structure.