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J. Biol. Chem., Vol. 276, Issue 8, 5556-5562, February 23, 2001

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The C Terminus of Mammalian Phospholipase D Is Required for Catalytic Activity^*

Mu-Ya Liu, Stephen Gutowski, and Paul C. Sternweis

From the Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, Texas 75235-9041

The activity of phospholipase D (PLD) is regulated by a variety of hormonal stimuli and provides a mechanistic pathway for response of cells to extracellular stimuli. The two identified mammalian PLD enzymes possess highly homologous C termini, which are required for catalytic activity. Mutational analysis of PLD1 and PLD2 reveals that modification of as little as the C-terminal threonine or the addition of a single alanine attenuates activity of the enzyme. Protein folding appears to be intact because mutant enzymes express to similar levels in Sf9 cells and addition of peptides representing the C-terminal amino acids, including the simple hexamer PMEVWT, restores partial activity to several of the mutants. Analysis of several mutants suggests a requirement for the hydrophobic reside at the 2-position but not an absolute requirement for the hydroxyl side chain of threonine at the C terminus. The inability of peptides amidated at their C termini to effect restoration of activity indicates the involvement of the C-terminal  carboxyl group in functional activity of these enzymes. The ability of peptides to restore activity to PLD enzymes mutated at the C terminus suggests a flexible interaction of this portion of the molecule with a catalytic core constructed on conserved HKD motifs. Participation of these C termini residues in either stabilization of the catalytic site or the enzymatic reaction itself remains to be determined. This requirement for the C terminus provides an excellent potential site for interaction with regulatory proteins that may either enhance or down-regulate the activity of these enzymes in vitro.

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