Abstract
Human phospholipid scramblase 3 (hPLSCR3) is a single pass transmembrane protein that plays a vital role in fat metabolism, mitochondrial function, structure, maintenance and apoptosis. The mechanism of action of scramblases remains still unknown, and the role of scramblases in phospholipid translocation is heavily debated. hPLSCR3 is the only member of scramblase family localized to mitochondria and is involved in cardiolipin translocation at the mitochondrial membrane. Direct biochemical evidence of phospholipid translocation by hPLSCR3 is yet to be reported. Functional assay in synthetic proteoliposomes upon Ca2+ and Mg2+ revealed that, apart from cardiolipin, recombinant hPLSCR3 translocates aminophospholipids such as NBD-PE and NBD-PS but not neutral phospholipids. Point mutation in hPLSCR3 (F258V) resulted in decreased Ca2+ binding affinity. Functional assay with F258V-hPLSCR3 led to ~50% loss in scramblase activity in the presence of Ca2+ and Mg2+. Metal ion-induced conformational changes were monitored by intrinsic tryptophan fluorescence, circular dichroism, surface hydrophobicity changes and aggregation studies. Our results revealed that Ca2+ and Mg2+ bind to hPLSCR3 and trigger conformational changes mediated by aggregation. In summary, we suggest that the metal ion-induced conformational change and the aggregation of the protein are essential for the phospholipid translocation by hPLSCR3.
Acknowledgements
The authors wish to thank Department of Science and Technology, Government of India and Indian Institute of Technology Madras for Circular Dichroism studies. S.K.P., U.S. and S.M. wish to thank Ministry of Human Resource Development (MHRD), Government of India and Indian Institute of Technology Madras for fellowship.
Conflict of interest statement: The authors declare no conflicts of financial interest in this study.
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