Catalytic action of fuculose 1-phosphate aldolase (class II) as derived from structure-directed mutagenesis

Previous analyses established the structures of unligated L-fuculose 1-phos phate aldolase and of the enzyme ligated with an inhibitor mimicking the su bstrate dihydroxyacetone phosphate. These data allowed us to suggest a cata lytic mechanism. On the basis of this proposal, numerous mutations were now introduced at the active center and tested with respect to their catalytic rates and their product distributions. For several mutants, the structures were determined. The results demonstrate the catalytic importance of some particular residues in defined conformations and in the mobile C-terminal c hain end. Moreover, they led to a modification of the proposed mechanism. T he effect of some mutations on enantioselectivity and on the ratio of diast ereomer formation indicates clearly the binding site of the aldehyde moiety in relation to the other substrate dihydroxyacetone phosphate.