Identification of a Drosophila vitamin K-dependent γ-glutamyl carboxylase

Abstract

Using reduced vitamin K, oxygen, and carbon dioxide, γ-glutamyl carboxylase post-translationally modifies certain glutamates by adding carbon dioxide to the position of those amino acids. In vertebrates, the modification of glutamate residues of target proteins is facilitated by an interaction between a propeptide present on target proteins and the γ- glutamyl carboxylase. Previously, the gastropod Conus was the only known invertebrate with a demonstrated vitamin K-dependent carboxylase. We report here the discovery of a γ-glutamyl carboxylase in Drosophila. This Drosophila enzyme is remarkably similar in amino acid sequence to the known mammalian carboxylases; it has 33% sequence identity and 45% sequence similarity to human γ-glutamyl carboxylase. The Drosophila carboxylase is vitamin K-dependent, and it has a K(m) toward a model pentapeptide substrate, FLEEL, of about 4 mM. However, unlike the human γ-glutamyl carboxylase, it is not stimulated by human blood coagulation factor IX propeptides. We found the mRNA for Drosophila γ-glutamyl carboxylase in virtually every embryonic and adult stage that we investigated, with the highest concentration evident in the adult head.