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. 2009 Oct;1790(10):1274-81.
doi: 10.1016/j.bbagen.2009.06.008. Epub 2009 Jun 18.

Calcium Binding Studies of Peptides of Human Phospholipid Scramblases 1 to 4 Suggest That Scramblases Are New Class of Calcium Binding Proteins in the Cell

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Calcium Binding Studies of Peptides of Human Phospholipid Scramblases 1 to 4 Suggest That Scramblases Are New Class of Calcium Binding Proteins in the Cell

Santosh Kumar Sahu et al. Biochim Biophys Acta. .

Abstract

Background: Phospholipid scramblases are a group of four homologous proteins conserved from C. elegans to human. In human, two members of the scramblase family, hPLSCR1 and hPLSCR3 are known to bring about Ca2+ dependent translocation of phosphatidylserine and cardiolipin respectively during apoptotic processes. However, affinities of Ca2+/Mg2+ binding to human scramblases and conformational changes taking place in them remains unknown.

Methods: In the present study, we analyzed the Ca2+ and Mg2+ binding to the calcium binding motifs of hPLSCR1-4 and hPLSCR1 by spectroscopic methods and isothermal titration calorimetry.

Results: The results in this study show that (i) affinities of the peptides are in the order hPLSCR1>hPLSCR3>hPLSCR2>hPLSCR4 for Ca2+ and in the order hPLSCR1>hPLSCR2>hPLSCR3>hPLSCR4 for Mg2+, (ii) binding of ions brings about conformational change in the secondary structure of the peptides. The affinity of Ca2+ and Mg2+ binding to protein hPLSCR1 was similar to that of the peptide I. A sequence comparison shows the existence of scramblase-like motifs among other protein families.

Conclusions: Based on the above results, we hypothesize that the Ca2+ binding motif of hPLSCR1 is a novel type of Ca2+ binding motif.

General significance: Our findings will be relevant in understanding the calcium dependent scrambling activity of hPLSCRs and their biological function.

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