The negative charge of the membrane has opposite effects on the membrane entry and exit of pH-low insertion peptide.

The pH-low insertion peptide (pHLIP) targets acidic diseases such as cancer. The acidity of the environment causes key aspartic acids in pHLIP to become protonated, causing the peptide to insert into membranes. Here we investigate how the negative charge of the membrane influences how pHLIP enters and exits the lipid bilayer. We found that electrostatic repulsion affected differently the membrane entry and exit of pHLIP for negatively charged membranes. As a consequence, a large hysteresis was observed. We propose this is not a consequence of structural changes but results from local changes in the environment of aspartic acids, shifting their pK values.

A novel pH-dependent membrane peptide that binds to EphA2 and inhibits cell migration.

Misregulation of the signaling axis formed by the receptor tyrosine kinase (RTK) EphA2 and its ligand, ephrinA1, causes aberrant cell-cell contacts that contribute to metastasis. Solid tumors are characterized by an acidic extracellular medium. We intend to take advantage of this tumor feature to design new molecules that specifically target tumors. We created a novel pH-dependent transmembrane peptide, TYPE7, by altering the sequence of the transmembrane domain of EphA2. TYPE7 is highly soluble and interacts with the surface of lipid membranes at neutral pH, while acidity triggers transmembrane insertion. TYPE7 binds to endogenous EphA2 and reduces Akt phosphorylation and cell migration as effectively as ephrinA1. Interestingly, we found large differences in juxtamembrane tyrosine phosphorylation and the extent of EphA2 clustering when comparing TYPE7 with activation by ephrinA1. This work shows that it is possible to design new pH-triggered membrane peptides to activate RTK and gain insights on its activation mechanism.