Substrate spectrum of l-rhamnulose kinase related to models derived from two ternary complex structures

The enzyme l-rhamnulose kinase from Escherichia coli participates in the degradation pathway of l-rhamnose, a common natural deoxy-hexose. The structure of the enzyme in a ternary complex with its substrates ADP and l-rhamnulose has been determined at 1.55 Å resolution and refined to Rcryst/Rfree values of 0.179/0.209. The result was compared with the lower resolution structure of a corresponding complex containing l-fructose instead of l-rhamnulose. In light of the two established sugar positions and conformations, a number of rare sugars have been modeled into the active center of l-rhamnulose kinase and the model structures have been compared with the known enzymatic phosphorylation rates. Rare sugars are of rising interest for the synthesis of bioactive compounds.