Tree of the month: Alcohol dehydrogenase from Saccharomyces cerevisiae

The Brewer, designed and engraved in the Sixteenth Century, by J. Amman.When we think about domestication, the first thing it comes to our mind is the image of beloved pets or farm animals. Some may even think about the species of plants humanity has harvested since long ago. There is, however, a humble fungus whose shared history with humanity is as ancient as agriculture itself and for which domestication has marked its biology in a way that few other organisms can compare with. Saccharomyces cerevisiae, the baker’s yeast, has been used to alter some foods’ properties for thousands of years, with incommensurable impact in our daily life. Beer, wine and other beverages have been all with us along history. Beer production was regulated by the ancient mesopotamian Code of Hammurabi and was systematically studied by Louis Pasteur centuries later, giving birth to the foundations of microbiology. Given its economical relevance, the easiness of its culture, and many other unique features of its biology, S. cerevisiae rapidly became one of the most popular model organisms for biological research, a trend that gave this little buddy the honour of being the first eukaryotic genome sequenced in 1996.


All this success is derived from some important facts. First of all, S. cerevisiae is an avid producer of ethanol even in oxygenic conditions, as long as the substrate concentration is high enough. While its growth speed cannot compete with bacteria in most media, under high osmotic pressures the yeast can do it. In fact, these conditions, common in fruit juices and malted cereals used for beverage production, allows yeast to outgrow most bacterial populations. As result of its metabolism, yeast produces ethanol which highly valued for humans and inhibits the growth of many bacterial organisms.


In the root of this metabolic wonder lies the enzyme ethanol dehydrogenase ADH1 that catalyzes the last step in the ethanol production pathway. Zinc-dependent ethanol dehydrogenases are widespread in the eukaryotic tree of life, present in plants, fungi and animals. The enzyme can be both catabolic and anabolic, with the first being more commonly found and used to detoxify alcohols, which is the function of the human homolog. Seven isoforms exist in S. cerevisiae that have different functions, with ADH1 being the responsible of most of the ethanolic production under normal circumstances. As we can see in our tree of the month, the genes involved in this metabolic step have been gained and lost many times in the evolution of fungi. In the Saccharomyces lineage several duplication events can be traced back to an ancient whole genome duplication event. Such evolutionary events have greatly modulated  S. cerevisae as the ultimate ethanol producer.

You can browse this tree and many more in the Saccharomyces cerevisiae phylome in the context of 12 completely sequenced fungal genomes here at phylome 4.