Expression, Purification, and Characterization of a Predicted Drosophila Glutaminyl Cyclase

Abstract

Glutaminyl cyclase (QC) is responsible for the N-terminal conversion of glutamine to pyroglutamate in many peptides. Though the N-terminal pyroglutamate is found in many different peptides in virtually all species, including Drosophila, QC activity has not been linked to this peptide modification in Drosophila. Sequence analyses revealed putative protein sequences in Drosophila with greater than 50% sequence homology to human QC. To evaluate the enzymatic activity of the predicted Drosophila QC sequence a bacterial fusion protein was designed which contained the predicted amino acid sequence for Drosophila QC along with a purification tag. Expression of the fusion protein and subsequent purification revealed a protein of the expected size of 44kD. The 44kD protein was evaluated using two previously published QC activity assays. Both assays revealed QC activity in the fusion protein similar to human QC as well similar inhibition with published QC inhibitors suggesting the Drosophila protein is a QC. Further analyses will be completed to compare the structural properties of the Drosophila QC to the human QC.