Dataset Information

Polar/Ionizable residues in transmembrane segments: effects on helix-helix packing.

ABSTRACT: The vast majority of membrane proteins are anchored to biological membranes through hydrophobic ?-helices. Sequence analysis of high-resolution membrane protein structures show that ionizable amino acid residues are present in transmembrane (TM) helices, often with a functional and/or structural role. Here, using as scaffold the hydrophobic TM domain of the model membrane protein glycophorin A (GpA), we address the consequences of replacing specific residues by ionizable amino acids on TM helix insertion and packing, both in detergent micelles and in biological membranes. Our findings demonstrate that ionizable residues are stably inserted in hydrophobic environments, and tolerated in the dimerization process when oriented toward the lipid face, emphasizing the complexity of protein-lipid interactions in biological membranes.

SUBMITTER: Bano-Polo M

PROVIDER: S-EPMC3440369 | biostudies-literature | 2012

REPOSITORIES: biostudies-literature

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Polar/Ionizable residues in transmembrane segments: effects on helix-helix packing.

Bañó-Polo Manuel M Baeza-Delgado Carlos C Orzáez Mar M Marti-Renom Marc A MA Abad Concepción C Mingarro Ismael I

PloS one 20120912 9

The vast majority of membrane proteins are anchored to biological membranes through hydrophobic α-helices. Sequence analysis of high-resolution membrane protein structures show that ionizable amino acid residues are present in transmembrane (TM) helices, often with a functional and/or structural role. Here, using as scaffold the hydrophobic TM domain of the model membrane protein glycophorin A (GpA), we address the consequences of replacing specific residues by ionizable amino acids on TM helix ...[more]

PMID: 22984481

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Project description:The ability of hydrophilic residues to shift the transverse position of transmembrane (TM) helices within bilayers was studied in model membrane vesicles. Transverse shifts were detected by fluorescence measurements of the membrane depth of a Trp residue at the center of a hydrophobic sequence. They were also estimated from the effective length of the TM-spanning sequence, derived from the stability of the TM configuration under conditions of negative hydrophobic mismatch. Hydrophilic residues (at the fifth position in a 21-residue hydrophobic sequence composed of alternating Leu and Ala residues and flanked on both ends by two Lys) induced transverse shifts that moved the hydrophilic residue closer to the membrane surface. At pH 7, the dependence of the extent of shift upon the identity of the hydrophilic residue increased in the order: L < G approximately = Y approximately = T < R approximately = H < S < P < K < E approximately = Q < N < D. By varying pH, shifts with ionizable residues fully charged or uncharged were measured, and the extent of shift increased in the order: L < G approximately = Y approximately = H(o) approximately = T < E(o) approximately = R < S < P < K+ < Q approximately = D(o) approximately = H+ < N approximately = E- < D-. The dependence of transverse shifts upon hydrophilic residue identity was consistent with the hypothesis that shift magnitude is largely controlled by the combination of side chain hydrophilicity, ionization state, and ability to position polar groups near the bilayer surface (snorkeling). Additional experiments showed that shift was also modulated by the position of the hydrophilic residue in the sequence and the hydrophobicity of the sequence moved out of the bilayer core upon shifting. Combined, these studies show that the insertion boundaries of TM helices are very sensitive to sequence, and can be altered even by weakly hydrophilic residues. Thus, many TM helices may have the capacity to exist in more than one transverse position. Knowledge of the magnitudes of transverse shifts induced by different hydrophilic residues should be useful for design of mutagenesis studies measuring the effect of transverse TM helix position upon function.

Dataset Information

Polar/Ionizable residues in transmembrane segments: effects on helix-helix packing.

Publications

Polar/Ionizable residues in transmembrane segments: effects on helix-helix packing.

Similar Datasets

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