Protein engineering and comparison of microbial expression systems of the biopharmaceutical L-asparaginase

Abstract

L-asparaginase (L-ASNase) is a biopharmaceutical widely used in treating leukemia, especially in Brazil. However, the available commercial formulations are comprised of proteins from bacterial origin, present high molecular weight and they are active only when tetrameric. Thus, problems such as uniformity in drug formulation, allergic reactions and silent inactivation of the enzyme by antibodies binding or serum clearance are found in relation to this biopharmaceutical. This project proposes obtaining micro-organisms that over-express L-ASNase enzyme with improved characteristics by analyzing the effect of the inclusion of post-translational modifications such as glycosylation. To achieve this goal, the strategies will be followed: cloning of L-ASNases in eukaryotic expression system, characterization and comparison of activities and stabilities of these enzymes with and without post-translational modification. The asparaginases chosen for group studies are from bacterial Escherichia coli and Erwinia chrysanthemi. The eukaryotic system that will be tested are conventional strain of Pichia pastoris (GS115) and the Glycoswitch system (P. pastoris strain of genetically modified that performs humanized glycosylation). Only the most promising isoforms in relation to the kinetic characteristics will be evaluated in parallel to their antitumor activity and stability in the presence of human serum in vitro. Insertion of humanized post-translational modifications might be a promising strategy for masking stimulatory epitopes of the human immune system and sites of cysteine-proteases already identified as responsible for the serum clearance in patients. Thus, artificial glycosylation sites may be inserted and evaluated with promising improvement of the biopharmaceutical characteristics. (AU)