A study of Pb2+ induced unfolding and aggregation of arginine kinase from Euphausia superba: kinetics and computational simulation integrating study

Arginine kinase is a crucial phosphagen kinase in invertebrates, which is associated to the environmental stress response, plays a key role in cellular energy metabolism. In this study, we investigated the Pb2+-induced inhibition and aggregation of Euphausia superba arginine kinase (ESAK) and found that significantly inactivated ESAK in a dose-dependent manner (IC50 = 0.058 +/- 0.002 mM). Spectrofluorimetry results showed that Pb2+ induced tertiary structural changes via the internal polarity increased and the non-polarity decreased in ESAK and directly induced ESAK aggregation. The ESAK aggregation process induced by Pb2+ occurred with multi-phase kinetics. The addition of osmolytes did not show protective effect on Pb2+-induced inactivation of ESAK. The computational molecular dynamics (MD) simulation showed that three Pb2+ interrupt the entrance of the active site of ESAK and it could be the reason on the loss of activity of ESAK. Several important residues of ESAK were detected that were importantly contributed the conformation and catalytic function of ESAK. Our study showed that Pb2+-induced misfolding of ESAK and the complete loss of activity irreversibly, which cannot be recovered by osmolytes. Communicated by Ramaswamy H. Sarma