Dihydroxyacetone kinases in Saccharomyces cerevisiae are involved in detoxification of dihydroxyacetone

The genes YML070W/DAK1 and YFL053W/DAK2 in the yeast Saccharomyces cerevisiae were characterized by a combined genetic and biochemical approach that firmly functionally classified their encoded proteins as dihydroxyacetone kinases (DAKs), an enzyme present in most organisms. The kinetic properties of the two isoforms were similar, exhibiting K-m(DHA) of 22 and 5 mum and K-m(ATP) of 0.5 and 0.1 mm for Dak1p and Dak2p, respectively. We furthermore show that their substrate, dihydroxyacetone (DRA), is toxic to yeast cells and that the detoxification is dependent on functional DAK. The importance of DAK was clearly apparent for cells where both isogenes were deleted (dak1Deltadak2Delta), since this strain was highly sensitive to DRA. In the opposite case, overexpression of either DAK1 or DAK2 made the dak1Deltadak2Delta highly resistant to DHA. In fact, overexpression of either DAK provided cells with the capacity to grow efficiently on DRA as the only carbon and energy source, with a generation time of about 5 h. The DRA toxicity was shown to be strongly dependent on the carbon and energy source utilized, since glucose efficiently suppresses the lethality, whereas galactose or ethanol did so to a much lesser extent. However, this suppression was found not to be explained by differences in DHA uptake, since uptake kinetics revealed a simple diffusion mechanism with similar capacity independent of carbon source. Salt addition strongly aggravated the DRA toxicity, independent of carbon source. Furthermore, the DHA toxicity was not linked to the presence of oxygen or to the known harmful agents methylglyoxal and formaldehyde. It is proposed that detoxification of DRA may be a vital part of the physiological response during diverse stress conditions in many species.