An Electrostatic/Hydrogen Bond Switch as the Basis for the Specific Interaction of Phosphatidic Acid with Proteins

Dirk T.S. Rijkers,Teun Munnik,Koert N.J. Burger,Edgar E. Kooijman,Ben de Kruijff,Christa Testerink,D. Peter Tieleman

doi:10.1074/jbc.m609737200

Dirk T.S. Rijkers, Teun Munnik + Show 5 more

Open Access

https://doi.org/10.1074/jbc.m609737200

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Abstract

Phosphatidic acid (PA) is a minor but important phospholipid that, through specific interactions with proteins, plays a central role in several key cellular processes. The simple yet unique structure of PA, carrying just a phosphomonoester head group, suggests an important role for interactions with the positively charged essential residues in these proteins. We analyzed by solid-state magic angle spinning 31P NMR and molecular dynamics simulations the interaction of low concentrations of PA in model membranes with positively charged side chains of membrane-interacting peptides. Surprisingly, lysine and arginine residues increase the charge of PA, predominantly by forming hydrogen bonds with the phosphate of PA, thereby stabilizing the protein-lipid interaction. Our results demonstrate that this electrostatic/hydrogen bond switch turns the phosphate of PA into an effective and preferred docking site for lysine and arginine residues. In combination with the special packing properties of PA, PA may well be nature's preferred membrane lipid for interfacial insertion of positively charged membrane protein domains.

Highlights

The Phosphatidic acid (PA) binding domains far identified and more recently [7]) are diverse and share no apparent sequence homology, in contrast to other lipid binding domains, such as e.g. the PH, PX, FYVE, and C2 domains [11,12,13,14,15]
We subsequently showed that the main cause behind this increase in negative charge of PA is hydrogen bond formation between the lysine or arginine side chains and the phosphomonoester head group of PA
The existence of hydrogen bonds between the mono- and di-anionic phosphate of PA and lysine and arginine side chains was further confirmed by MD simulation

Summary

Introduction

The PA binding domains far identified (for review, see Ref. 10) and more recently [7]) are diverse and share no apparent sequence homology, in contrast to other lipid binding domains, such as e.g. the PH, PX, FYVE, and C2 domains [11,12,13,14,15]. The negatively charged phosphomonoester head group of PA would be expected to interact electrostatically with basic amino acids in a lipid binding domain. We provided evidence that competing hydrogen bonds, e.g. from the primary amine of the head group of phosphatidylethanolamine (PE), can destabilize this intramolecular hydrogen bond and, favor the further deprotonation, i.e. increase the negative charge, of PA [8] These data raised the intriguing hypothesis that a combination of electrostatic and hydrogen bond interactions and not just electrostatic interactions of PA with basic amino acids, i.e. lysine and arginine, forms the basis of the (specific) binding of PA to PA-binding proteins. We propose that the electrostatic/hydrogen bond switch provided by the phosphomonoester is a universal mechanism in stabilizing the binding of phosphomonoesters to proteins

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