Characterization of a novel Glutaminase-free L-asparaginase from Bifidobacterium thermophilum.

L-asparaginase (ASNase), as a pivotal amidohydrolase enzyme, has been used in removing acrylamide in food processing and treating acute lymphoblastic leukemia in clinic. In this study, a novel ASNase from Bifidobacterium thermophilum (BtASNase) was successfully cloned and heterologously expressed in Escherichia coli. BtASNase was identified to share maximum 40% structural similarity with other ASNases in PDB database. The purified BtASNase with monomeric size about 35 kDa had the highest specific activity (554.82 IU/mg) at 55 °C and pH 8.0. Further investigation indicated that BtASNase showed great stability at wide pH range (6.0-11.0), and retained more than 85% of its activity for 50 min at 37 °C. To be noted, BtASNase exhibited high L-asparaginase specificity and zero glutaminase activity. To our knowledge, this is a novel exploration of ASNase from Bifidobacterium thermophilum, and the explored BtASNase could be a potential candidate with desirable advantages for overcoming limitations such as glutaminase activity, narrow pH range stability, and low thermostability restrict in industry applications of ASNase.