Biochemical characterization of Drosophila[gamma]-glutamyl carboxylase and its role in fly development

To investigate structure-function relationships in [gamma]-glutamyl carboxylases, the enzyme from Drosophila melanogaster was characterized. Four cysteine residues were shown to be important determinants for enzymatic activity. Native Drosophila substrates have not yet been identified, but propeptides of human prothrombin and factor IX are recognized by the Drosophila enzyme. The presence of the propeptide region increased apparent affinity by [approximately]200-fold, and mutation of a hydrophobic residue of factor IX propeptide (F-16A) decreased carboxylation by 90%, as in the human enzyme. Substrate recognition appears to be highly conserved between the human and Drosophila[gamma]-glutamyl carboxylases. Inactivation of Drosophila[gamma]-glutamyl carboxylase by non-sense mutations or insertional mutagenesis by P-element insertion have no apparent effects on growth and fertility under laboratory conditions.