Supersensitive phospholipid sensing

Alysine-laden sensor makes an actin regulator ultrasensitive to phospholipid levels, according to Venizelos Papayannopoulos, Wendell Lim (University of California, San Francisco, CA), and colleagues.

Phospholipids, particularly PIP₂, are activators of N-WASP—an Arp2/3 regulator that turns on actin polymerization. None of the common PIP-binding domains (e.g., Pleckstrin Homology or Phox domains) are found in N-WASP. Instead, a region of 10 basic residues (the B motif) binds to the phospholipids. The new research reveals that this conglomerate of positive charges turns N-WASP into an all-or-nothing switch in response to changing PIP₂ density.

At 10% PIP₂, N-WASP bound tenfold more strongly to vesicles than it did at 2% PIP₂. Even sharper effects from lipid density were seen in actin polymerization...