Investigation of the interaction of m-calpain with phospholipids: calpain-phospholipid interactions

Phosphatidyl inositol, phosphatidyl choline, phosphatidyl glycerol, phosphatidyl serine, phosphatidyl ethanolamine, phosphatidic acid and sphingomyelin were all found to be effective at reducing the Ca²⁺ requirement for m-calpain autolysis. In the absence of phospholipid, pig kidney m-calpain required 1.4 mM Ca²⁺ for 50% autolysis under the assay conditions used. Phospholipids caused a reduction in this Ca²⁺ requirement to a value between 0.45 mM Ca²⁺ for phosphatidyl glycerol and 1.1 mM Ca²⁺ for phosphatidyl ethanolamine. Previous studies (Crawford, C., Brown, N.R. and Willis, A.C. (1990) Biochem. J. 265, 575-579) have shown that the most probable site for phospholipid interaction in calpain is the N-terminal region between residues 39 to 62 of the small subunit of calpain (G₁₇TAMRILGG). In this study we examine the possible role of this G₁₇TAMRILGG region. Three synthetic peptides corresponding to parts of this sequence were used to examine the phospholipid binding sequence. Analysis of the phospholipid vesicle binding properties of these peptides suggested that both the TAMRIL and polyglycine sequences were required for binding to phosphatidyl inositol vesicles.