The Interaction of Hsp70 with Phosphatidylserine Membranes is Mediated by a Highly Positive Region of the Molecule

Abstract

Heat shock proteins (hsp) participate in many cellular processes during normal physiological conditions. In particular, they are involved in protein folding and are referred to as molecular chaperones. During stress conditions, hsp participate in the repair and recovery from an insult and confer protection from subsequent stresses. In addition, they are released into the extracellular milieu where they act as signaling molecules directed at activating the immune system to avoid the propagation of the insult. Hsp70, the major inducible form of the hsp family, does not contain any consensus secretory signal that predicts its export via the classical ER-Golgi secretory pathway. The proposed mechanism for the release of Hsp70 requires an initiated translocation into the plasma membrane. However, Hsp70 does not contain any hydrophobic domain that can predict its insertion into lipid membranes. Using an in vitro liposome insertion assay, we have determined that Hsp70 displays selectivity for negatively charge lipids and its insertion is enhanced by a decrease in the membrane fluidity. The region that is inserted into the lipid membrane has been mapped toward the C-terminus end, which contains the peptide binding domain. Lipid recognition/insertion requires a highly positive region on the molecule. Finally, the addition of ADP, but not ATP, reduced membrane insertion, suggesting that the interaction with the lipid bilayer is dependent on the conformation of the molecule.Supported by NIH R01 GM098455.