Transmembrane vs. non-transmembrane hydrophobic helix topography in model and natural membranes

London, Erwin; Shahidullah, Khurshida

doi:10.1016/j.sbi.2009.07.007

Cited by 23 publications

(16 citation statements)

References 72 publications

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“…Another possibility is unfolding of part of the helix, followed by immediate exit of the polypeptide from the membrane, which leads to a thinning of the lipid bilayer around the shortened helical part of the peptide. This suggestion is based on recent findings that the lipid bilayer can accommodate short helices with a minimal energetic cost (17,18). Further propagation of the helix-coil transition is accompanied by a rapid exit of part of the polypeptide within the next 5 msec (UI 2 ).…”

Section: Discussionmentioning

confidence: 99%

pH (low) insertion peptide (pHLIP) inserts across a lipid bilayer as a helix and exits by a different path

Andreev

Karabadzhak

Weerakkody

et al. 2010

Proc. Natl. Acad. Sci. U.S.A.

148

197

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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.folding kinetics | helix formation | lipid-peptide interaction | membranes | transmembrane helix

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Section: Discussionmentioning

confidence: 99%

pH (low) insertion peptide (pHLIP) inserts across a lipid bilayer as a helix and exits by a different path

Andreev

Karabadzhak

Weerakkody

et al. 2010

Proc. Natl. Acad. Sci. U.S.A.

148

197

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“…mTMDs occur in membrane proteins and are unique in that they can assume two different topologies. These involve either movement of helices in and out of the bilayer, or reorientation of helices within the bilayer after insertion (81- 83). This orientation change is a direct consequence of the presence of polar residues, including Asp and Glu, which reduce their hydrophobicity compared to standard TMD (81-83).…”

Section: Discussionmentioning

confidence: 99%

“…These involve either movement of helices in and out of the bilayer, or reorientation of helices within the bilayer after insertion (81- 83). This orientation change is a direct consequence of the presence of polar residues, including Asp and Glu, which reduce their hydrophobicity compared to standard TMD (81-83). Some examples of proteins that have shown dual topology and mTMDs are the human aquaporin water channel APQ1, the hepadnaviral large envelope protein, and the ATP-gated ion channel subunit P2X2 (along with the related ASIC protein) (84-86).…”

Section: Discussionmentioning

confidence: 99%

PS membrane asymmetry influences the folding and insertion of a transmembrane helix

Scott

Heberle

Katsaras³

et al. 2018

Preprint

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The plasma membrane (PM) contains an asymmetric distribution of lipids between the inner and outer leaflets of its bilayer. A lipid of special interest in eukaryotic cells is the negatively charged phosphatidylserine (PS). In healthy cells, PS is actively sequestered to the inner leaflet of the PM but can redistribute to the outer leaflet when the cell is damaged or at the onset of apoptosis. The influence of PS asymmetry and its loss on membrane protein structure and organization have not been widely addressed. Marginally hydrophobic membrane proteins contain acidic residues in their transmembrane sequence, which can enable topological transitions after membrane association. The pH low insertion peptide (pHLIP), which undergoes a topological reorientation and inserts into the membrane at acidic pH -as its name implies, is a useful and well-characterized model for studying these transitions. Although it is known that the inclusion of PS in symmetric vesicles affects the membrane insertion process of pHLIP by lowering the pH midpoint of insertion, it is unclear how PS asymmetry influences these topological transitions. Here, we studied pHLIP's topology using freely-floating asymmetric phosphatidylcholine (PC)/PS vesicles with PS enriched in the inner leaflet. We developed a modified protocol to create asymmetric vesicles containing PS and employed Annexin V labeled with an Alexa 568 fluorophore as a new probe to quantifying PS asymmetry. For pHLIP, membrane insertion was affected by the surface charge difference between bilayer leaflets caused by the asymmetric distribution of charged lipids between the leaflets. We thus conclude that lipid asymmetry can have consequences for the behavior of membrane-associated proteins.A corollary is that model studies using symmetric bilayers to mimic the PM may fail to capture important aspects of protein-membrane interactions. 5 symmetric PS vesicles, our lab previously showed that both the insertion pK and the insertion depth in State II decreased with increasing PS concentration (27). We proposed that both observations can be explained by an unfavorable interaction between the negatively charged PS head group and the seven negative charges present on pHLIP at neutral pH (27). However, it is unknown how a more biologically faithful model system, one in which PS is enriched in the inner leaflet, would influence pHLIP insertion. To test this, we modified a technique for producing freely-floating vesicles in order to mimic the asymmetric distribution of PS in the PM (28). We found that PS asymmetry caused an increase in the midpoint of pHLIP insertion, suggesting that for a physiologically relevant transbilayer charge distribution-i.e., less negative charge in the outer compared to the inner leaflet-lowers the energetic barrier for insertion. This finding proposes a general role for PS asymmetry in promoting the folding of TM proteins. 6 Materials and MethodsMaterials. The lipids 1-palmitoyl-d31-2-oleoyl-sn-glycero-3-phosphocholine (POPCd31), 1palmitoyl-2-oleoyl-sn-glycero-3-pho...

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“…The middle part is a moderately polar sequence that contains protonatable residues, and is the environment-sensitive, membrane inserting part of the peptide. Recent studies show that the transmembrane helix might be as short as 15 residues (London and Shahidullah, 2009), therefore we assume that the membrane-inserting sequences might consist of ~15 to 25 amino acids. The other two blocks are the two flanking sequences.…”

Section: Phlip Represents Phlips Are a New Class Of Delivery Agentsmentioning

confidence: 99%

pH-sensitive membrane peptides (pHLIPs) as a novel class of delivery agents

Andreev

Engelman

Reshetnyak

2010

Molecular Membrane Biology

117

102

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Here we review a novel class of delivery vehicles based on pH-sensitive, moderately polar membrane peptides, which we call pH (Low) Insertion Peptides (pHLIPs), that target cells located in the acidic environment found in many diseased tissues, including tumors. SpecificAcidity targeting by pHLIPs is achieved as a result of helix formation and transmembrane insertion. In contrast to the earlier technologies based on cell-penetrating peptides, pHLIPs act as monomeric membrane-inserting peptides that translocate one terminus across a membrane into the cytoplasm, while the other terminus remains in the extracellular space, locating the peptide in the membrane lipid bilayer. Therefore,This geometry gives pHLIP has a dual delivery capability: it can tether cargo molecules or nanoparticles to the surfaces of cells in diseased tissues and/or it can move a cell-impermeable cargo molecule across the membrane into the cytoplasm. The source of energy for moving polar molecules attached to pHLIP through the hydrophobic layer of a membrane bilayer is the membrane-associated folding of the polypeptide. A drop in pH leads to the protonation of negatively charged residues (Asp or Glu), which enhances peptide hydrophobicity, increasing the affinity of the peptide for the lipid bilayer and triggering peptide folding and subsequent membrane insertion. The process is accompanied by the release of energy that can be utilized to move cell-impermeable cargo across a membrane. That the mechanism is now understood, and that targeting of tumors in mice has been shown, suggest a number of future applications of the pHLIP technology in the diagnosis and treatment of disease.

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Transmembrane vs. non-transmembrane hydrophobic helix topography in model and natural membranes

Cited by 23 publications

References 72 publications

pH (low) insertion peptide (pHLIP) inserts across a lipid bilayer as a helix and exits by a different path

pH (low) insertion peptide (pHLIP) inserts across a lipid bilayer as a helix and exits by a different path

PS membrane asymmetry influences the folding and insertion of a transmembrane helix

pH-sensitive membrane peptides (pHLIPs) as a novel class of delivery agents

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