SHAPING OF DROSOPHILA ALCOHOL-DEHYDROGENASE THROUGH EVOLUTION - RELATIONSHIP WITH ENZYME FUNCTIONALITY

Drosophilidae is a large, widely distributed family of Diptera includi ng 61 genera, of which Drosophila is the most representative. Drosophi la feeding is part of the saprophytic trophic chain, because of its de pendence upon decomposing organic matter. Many species have adapted to fermenting fruit feeding or to artificial (man-made) fermentation hab itats, such as cellars and breweries. Actually, the efficient exploita tion of niches with alcohols is considered one of the reasons for the worldwide success of this genus. Drosophila alcohol dehydrogenase (ADH ), a member of the short-chain dehydrogenase/reductase family (SDR), i s responsible for the oxidation of alcohols, but its direct involvemen t in fitness, including alcohol tolerance and utilization, gives rise to much controversy. Thus, it remains unclear whether ADH differentiat ion through evolution is somehow associated with natural adaptation to new feeding niches, and thus maybe to Drosophila speciation, or if it is a simple reflection of neutral divergence correlated with time sep aration between species. To build a hypothesis which could shed light on this dilemma, we analyzed the amino acid variability found in the 5 7 protein ADH sequences reported up to now, identified the taxon-speci fic residues, and localized them in a three-dimensional ADH model. Our results define three regions whose shaping has been crucial for ADH d ifferentiation and would be compatible with a contribution of ADH to D rosophila speciation.