Bacterial L-asparaginases have been used as anti-
cancer drugs for over 4 decades though presenting, along with their therapeutic efficacy, several side effects due to their bacterial origin and, seemingly, to their secondary
glutaminase activity. Helicobacter pylori type II L-
asparaginase possesses interesting features, among which a reduced catalytic efficiency for L-GLN, compared to the drugs presently used in
therapy. In the present study, we describe some
enzyme variants with catalytic and in vitro cytotoxic activities different from the wild type
enzyme. Particularly, replacements on catalytic threonines (T16D and T95E) deplete the
enzyme of both its catalytic activities, once more underlining the essential role of such residues. One serendipitous mutant, M121C/T169M, had a preserved efficiency vs
L-asparagine but was completely unable to carry out
L-glutamine hydrolysis. Interestingly, this variant did not exert any cytotoxic effect on HL-60 cells. The M121C and T169M single mutants had reduced catalytic activities (nearly 2.5- to 4-fold vs wild type
enzyme, respectively). Mutant Q63E, endowed with a similar catalytic efficiency versus
asparagine and halved
glutaminase efficiency with respect to the wild type
enzyme, was able to exert a cytotoxic effect comparable to, or higher than, the one of the wild type
enzyme when similar
asparaginase units were used. These findings may be relevant to determine the role of
glutaminase activity of L-
asparaginase in the anti-proliferative effect of the
drug and to shed light on how to engineer the best
asparaginase/
glutaminase combination for an ever improved, patients-tailored
therapy.