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Li, J.Y. et al.

Studies of the role of the integrin EF-hand, Ca2+-binding sites in glycosylphosphatidylinositol-specific phospholipase D: reduced expression following mutagenesis of residues predicted to bind Ca2+.

Previous studies of glycosylphosphatidylinositol-specific phospholipase D (GPI-PLD) have demonstrated that GPI-PLD can bind Ca2+ ions with high specificity (J.-Y. Li, K. Hollfelder, K.-S. Huang, and M. G. Low, J. Biol. Chem. 269, 28063-28971, 1994). In this study the functional role of the bound Ca2+ ions was evaluated. The enzymatic activity of purified GPI-PLD, which was depleted of divalent cations by pretreatment with EDTA, EGTA, or 1, 10-phenanthroline, could be completely restored with Zn2+ (and partially with Co2+), which indicates that Ca2+ can be removed from the protein without affecting its enzymatic activity. This result suggested that Ca2+ bound to GPI-PLD has a structural or regulatory role but is not required for GPI hydrolysis. To evaluate these possibilities we transfected COS cells with GPI-PLD mutants in which the predicted Ca2+-binding sites were either deleted completely or altered by single-residue substitution. All of the mutations showed substantial reductions in the amount of GPI-PLD secreted into the medium (0-6% of wild type). The data indicate that bound Ca2+ plays an important role in the initial folding, intracellular transport, or secretion of GPI-PLD even though it has no discernible role in the mature, secreted protein.[1]

References

Studies of the role of the integrin EF-hand, Ca2+-binding sites in glycosylphosphatidylinositol-specific phospholipase D: reduced expression following mutagenesis of residues predicted to bind Ca2+. Li, J.Y., Low, M.G. Arch. Biochem. Biophys. (1999) [Pubmed]

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