Alcohol dehydrogenase class IV sigma chain
Homo sapiens (human)
If you had too much beer to drink and a bad hangover the next morning, this protein may be the one you should blame. Alcohols are chemical derivatives of alkanes, with a hydroxyl group (OH) replacing a hydrogen. Low-molecular weight alcohols, in particular methanol, can be quite toxic in themselves, but what cause hangover is not ethanol. Ethanol is converted in the body to acetaldehyde. It is acetaldehyde which causes the symptoms of hangover. Ethanol is the substrate for the protein alcohol dehydrogenase, the molecule that you see here, and acetaldehyde is the product. Alcohol dehydrogenase can also use methanol as a substrate. In that case the product is formaldehyde, a very potent poison. Methanol is therefore highly toxic and ethanol is actually an antidote against methanol poisoning. Bacteria in the stomach may produce alcohols as a result of their natural metabolism and alcohol dehydrogenase helps to dispose of such product: it was invented by nature to help you drink beer.
The catalytic reaction from ethanol to acetaldehyde involves two cofactors associated with the protein: nicotinamid-adenine-dinucleotide and zinc. Nicotinamid-adenine-dinucleotide (NAD) is a natural compound involved in many chemical processes and zinc helps the removal of an electron in the oxidation process of ethanol. In the structure here one can see the dimer of alcohol dehydrogenase, each with its copy of NAD and zinc. Next to the zinc atom is another small molecule, acetate. Acetate is the product of the conversion of acetaldehyde, however it appears in this structure just by chance. The function of bacterial alcohol dehydrogenases is the opposite of the human one. Instead of digesting alcohol, they create alcohol from other sources. This is called fermentation, used in the production of alcohols.
Protein Data Bank (PDB)
Author: Arno Paehler