Protein Kinase C-Dependent Phosphorylation of Human Pleckstrin Reduces its Capacity for Self-Association and Impairs its Ability to Bind Phosphoinositide

Abstract

Pleckstrin is a major substrate of protein kinase C in lymphocytes, macrophages, monocytes, granulocytes and platelets. In
these cells, pleckstrin is expressed at high levels and represents approximately 1 % of total cellular protein. Pleckstrin plays
an important role in protein kinase C-dependent secretion, and abberant pleckstrin phosphorylation has been associated
with disease. The mechanism, however, by which phosphorylation regulates pleckstrin function is unknown. Here, we show
that native pleckstrin self-associates to form dimers that reduce its binding capacity to phosphoinositides. Phosphomimetic
amino acid substitutions at residues normally phosphorylated by protein kinase C result in significantly reduced pleckstrin
dimerization. Although phosphomimetic forms of pleckstrin exhibit subtle conformational changes they retain most of their
phosphoinositide binding properties. These findings s