The Isolation of Native Glutaminyl Cyclase from Saccharomyces cerevisiae

Glutaminyl Cyclase (QC)(2.5.2.3) catalyzes the cyclization of the N-terminal glutamine residues of peptides and proteins. Recent interest in QC has been generated by studies that have linked QC activity in human neuroendocrine tissue to diseases such as Alzheimer’s and osteoporosis. While QC has been isolated and characterized in multiple mammalian species, no attempt has been made to isolate the QC protein present in Saccharomyces cerevisiae. Therefore, this study sought to isolate and begin the characterization of yeast QC protein. A purification scheme was constructed and activity assays were identified to measure QC activity in purified protein samples. Basic characterization of yQC included SDS-PAGE analysis and an imidazole inhibition assay. The results of the study indicate that QC was isolated from S. cerevisiae. QC activity was found to have a total activity of 306 nmol/hr using the spectrophotometric assay. QC activity was verified using a more specific fluorometric assay. Furthermore, the partially purified protein was shown to have a molecular mass of 41 kd, which correlates with the theoretical weight of the yQC. While the results of this study verify QC activity, further purification of yQC would allow for the sequence analysis of the isolated protein to conclusively verify its identity. Still, this study has determined a basic purification scheme to isolate QC from S. cerevisiae.