biostudies-literature00520Andreev OANCI NIH HHSNIGMS NIH HHSPHS HHS4081-6https://www.ebi.ac.uk/biostudies/studies/S-EPMC2840156biostudies-literatureUnknown107(9)What are the molecular events that occur when a peptide inserts across a membrane or exits from it? Using the pH-triggered insertion of the pH low insertion peptide to enable kinetic analysis, we show that insertion occurs in several steps, with rapid (0.1 sec) interfacial helix formation, followed by a much slower (100 sec) insertion pathway to give a transmembrane helix. The reverse process of unfolding and peptide exit from the bilayer core, which can be induced by a rapid rise of the pH from acidic to basic, proceeds approximately 400 times faster than folding/insertion and through different intermediate states. In the exit pathway, the helix-coil transition is initiated while the polypeptide is still inside the membrane. The peptide starts to exit when about 30% of the helix is unfolded, and continues a rapid exit as it unfolds inside the membrane. These insights may guide understanding of membrane protein folding/unfolding and the design of medically useful peptides for imaging and drug delivery.Proceedings of the National Academy of Sciences of the United States of AmericapH (low) insertion peptide (pHLIP) inserts across a lipid bilayer as a helix and exits by a different path.PMC2840156R01 CA133890R01 133890R01 GM073857Karabadzhak AGAndreev GOEngelman DMWeerakkody DReshetnyak YKAndreev OA52falsepH (low) insertion peptide (pHLIP) inserts across a lipid bilayer as a helix and exits by a different path.What are the molecular events that occur when a peptide inserts across a membrane or exits from it? Using the pH-triggered insertion of the pH low insertion peptide to enable kinetic analysis, we show that insertion occurs in several steps, with rapid (0.1 sec) interfacial helix formation, followed by a much slower (100 sec) insertion pathway to give a transmembrane helix. The reverse process of unfolding and peptide exit from the bilayer core, which can be induced by a rapid rise of the pH from acidic to basic, proceeds approximately 400 times faster than folding/insertion and through different intermediate states. In the exit pathway, the helix-coil transition is initiated while the polypeptide is still inside the membrane. The peptide starts to exit when about 30% of the helix is unfolded, and continues a rapid exit as it unfolds inside the membrane. These insights may guide understanding of membrane protein folding/unfolding and the design of medically useful peptides for imaging and drug delivery.2010-01-01T00:00:00Z2010 Mar2024-11-12T00:02:16.441Z2019-03-27T00:29:27ZS-EPMC28401562016011310.1073/pnas.0914330107