Assessment of structural behaviour of a new L-asparaginase and SAXS data-based evidence for catalytic activity in its monomeric form.

ABSTRACT

The present study reports the structural and functional characterization of a new glutaminase-free recombinant L-asparaginase (PrASNase) from Pseudomonas resinovorans IGS-131. PrASNase showed substrate specificity to L-asparagine, and its kinetic parameters, Km, Vmax, and kcat were 9.49 × 10-3 M, 25.13 IUmL-1 min-1, and 3.01 × 103 s-1, respectively. The CD spectra showed that PrASNase consisted of 18.5 % helix, 21.5 % antiparallel sheets, 4.2 % parallel sheets, 14 % turns, and rest other structures. FTIR was used for the functional characterization, and molecular docking predicted that the substrate interacts with serine, alanine, and glutamine in the binding pocket of PrASNase. Differing from known asparaginases, structural characterization by small-angle X-ray scattering (SAXS) and analytical ultracentrifugation (AUC) unambiguously revealed PrASNase to exist as a monomer in solution at low temperatures and oligomerized to a higher state with temperature rise. Through SAXS studies and enzyme assay, PrASNase was found to be mostly monomer and catalytically active at 37 °C. Furthermore, this glutaminase-free PrASNase showed killing effects against WIL2-S and TF-1.28 cells with IC50 of 7.4 µg.mL-1 and 5.6 µg.mL-1, respectively. This is probably the first report with significant findings of fully active L-asparaginase in monomeric form using SAXS and AUC and demonstrated the potential of PrASNase in inhibiting cancerous cells, making it a potential therapeutic candidate.