In most organisms, efficient D-galactose utilization is accomplished via a well-studied pathway known as the Leloir pathway. However, in some bacterial and fungal species, an alternative energy-yielding route has been identified, namely the De Ley-Doudoroff pathway. In this lesser-known route, D-galactose is metabolized in five consecutive reactions carried out by specific enzymes. Previously, none of the proteins belonging to this metabolic network had been characterized structurally. A crystal structure of a bacterial kinase that controls the fifth reaction is reported here for the first time. The protein bears unique structural elements that determine its biological function and substrate specificity. More »