The Cation-π Box is a Specific Phosphatidylcholine Membrane Targeting Motif

Summary
Peripheral membrane proteins can be  targeted to specific organelles or the plasma  membrane by differential recognition of  phospholipid headgroups. While molecular  determinants of specificity for several  headgroups, including phosphatidylserine  and phosphoinositides are well defined,  specific recognition of the headgroup of the  zwitterionic phosphatidylcholine (PC) is less  well understood. In cytosolic proteins the  cation-π box provides a suitable receptor for  choline recognition and binding through the  trimethylammonium moiety. In PC, this  moiety might provide a sufficient handle to  bind to peripheral proteins via a cation-π cage, where the π systems of two or more  aromatic residues are within 4-5 Å of the  quaternary amine. We prove this hypothesis  by engineering the cation-π box into secreted  phosphatidylinositol-specific phospholipase C  from Staphylococcus aureus, which lacks  specific PC recognition. The N254Y/H258Y  variant selectively binds PC-enriched vesicles,  and X-ray crystallography reveals  N254Y/H258Y binds choline and  dibutyroylphosphatidylcholine within the  cation-π motif. Such simple PC recognition  motifs could be engineered into a wide variety  of secondary structures providing a generally  applicable method for specific recognition of  PC.

This study is published online in the Journal of Biological Chemistry and is free to access.