pH (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.
Physics Department, University of Rhode Island, 2 Lippitt Road, Kingston, RI 02881, USA. andreev@mail.uri.edu
Oleg A
OA
Andreev
Alexander G
AG
Karabadzhak
Dhammika
D
Weerakkody
Gregory O
GO
Andreev
Donald M
DM
Engelman
Yana K
YK
Reshetnyak
D002942:Circular Dichroism; D006863:Hydrogen-Ion Concentration; D008051:Lipid Bilayers; D008565:Membrane Proteins / Q000737:chemistry*; D011487:Protein Conformation; D017510:Protein Folding; D013050:Spectrometry, Fluorescence; D013816:Thermodynamics
D008051:Lipid Bilayers; D008565:Membrane Proteins; C533201:pHLIP protein