Biochemical Evidence for Lead and Mercury Induced Transbilayer Movement of Phospholipids Mediated by Human Phospholipid Scramblase 1

Human phospholipid scramblase 1(hPLSCR1) is a transmembrane protein involved in bidirectional scrambling of plasma membrane phospholipids during cell activation, blood coagulation, and apoptosis in response to elevated intracellular Ca2+ levels. Pb2+ and Hg2+ are known to cause procoagulant activation via phosphatidylserine exposure to the external surface in erythrocytes, resulting in blood coagulation. To explore its role in lead and mercury poisoning, hPLSCR1 was overexpressed in Escherichia coli BL21 (DE3) and purified using affinity chromatography. The biochemical assay showed rapid scrambling of phospholipids in the presence of Hg2+ and Pb2+. The,binding constant (K-a) was calculated and found to be 250 nM(-1) and 170 nM(-1) for Hg2+ and Pb2+, respectively. The intrinsic tryptophan fluorescence and far ultraviolet circular dichroism studies revealed conformational changes. hPLSCR1 treated with protein modifying reagent N-ethylmaleimide before functional reconstitution showed 40% and 24% inhibition in the presence of Hg2+ and Pb2+, respectively. This is the first biochemical evidence to prove the above hypothesis that hPLSCR1 is activated in heavy metal poisoning, which leads to bidirectional transbilayer movement of phospholipids. that Hg2+ and Pb2+ bind to hPLSCR1. and induce