Insertion of Bacteriorhodopsin Helix C Variants into Biological Membranes
A peptide corresponding to bacteriorhodopsin (bR) helix C, later named pHLIP, inserts across lipid bilayers as a monomeric α-helix at acidic pH, but is an unstructured surface-bound monomer at neutral pH. As a result of such pH-responsiveness, pHLIP targets acidic tumors and has been used as a vehicle for imaging and drug-delivery cargoes. To gain insights about the insertion of bR helix C into biological membranes, we replaced two key aspartic residues that control the topological transition from the aqueous phase into a lipid bilayer. Here, we used an in vitro transcription–translation system to study the translocon-mediated insertion of helix C-derived segments into rough microsomes. Our…
Conformational clamping by a membrane ligand activates the EphA2 receptor
AbstractThe EphA2 receptor is a promising drug target for cancer treatment, since EphA2 activation can inhibit metastasis and tumor progression. It has been recently described that the TYPE7 peptide activates EphA2 using a novel mechanism that involves binding to the single transmembrane domain of the receptor. TYPE7 is a conditional transmembrane (TM) ligand, which only inserts into membranes at neutral pH in the presence of the TM region of EphA2. However, how membrane interactions can activate EphA2 is not known. We systematically altered the sequence of TYPE7 to identify the binding motif used to activate EphA2. With the resulting six peptides, we performed biophysical and cell migratio…
Controllable membrane remodeling by a modified fragment of the apoptotic protein Bax.
Intrinsic apoptosis is orchestrated by a group of proteins that mediate the coordinated disruption of mitochondrial membranes. Bax is a multi-domain protein that, upon activation, disrupts the integrity of the mitochondrial outer membrane by forming pores. We strategically introduced glutamic acids into a short sequence of the Bax protein that constitutively creates membrane pores. The resulting BaxE5 peptide efficiently permeabilizes membranes at acidic pH, showing low permeabilization at neutral pH. Atomic force microscopy (AFM) imaging showed that at acidic pH BaxE5 established several membrane remodeling modalities that progressively disturbed the integrity of the lipid bilayer. The AFM…