A Novel Soluble Peptide with pH-Responsive Membrane Insertion.

Several diseases, such as cancer, are characterized by acidification of the extracellular environment. Acidosis can be employed as a target to specifically direct therapies to the diseased tissue. We have used first principles to design an acidity-triggered rational membrane (ATRAM) peptide with high solubility in solution that is able to interact with lipid membranes in a pH-dependent fashion. Biophysical studies show that the ATRAM peptide binds to the surface of lipid membranes at pH 8.0. However, acidification leads to the peptide inserting into the lipid bilayer as a transmembrane α-helix. The insertion of ATRAM into membranes occurs at a moderately acidic pH (with a pK of 6.5), similar to the extracellular pH found in solid tumors. Studies with human cell lines showed a highly efficient pH-dependent membrane targeting, without causing toxicity. Here we show that it is possible to rationally design a soluble peptide that selectively targets cell membranes in acidic environments.

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.