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#membrane thickness

2 public questions tagged with this topic.

Properties of Plasma Membrane

Which of the following does NOT affect membrane thickness?

Thickness hydrocarbon core typically three to four nanometers varies with chemical features not cellular energy currency. Acyl chain length linearly increases thickness about one point five angstrom per CH2; cis double bond shortens effective length kink reducing thickness. Cholesterol ordering straightens chains increasing thickness about four angstroms in fluid membranes by extending acyl conformations and reducing gauche defects. Integral proteins impose hydrophobic mismatch leading local thickening thinning compensated tilting clustering recruitment matching lipids as shown for SERCA rhodopsin potassium channels. Experiments X ray scattering small angle neutron scattering AFM confirm adjustments. ATP concentrations regulate activity P type ATPases ABC transporters flippases actin polymerization remodeling domains but do not change hydrocarbon chain length chemically. Depleting ATP halts active asymmetry yet freeze fracture electron microscopy shows lamellar thickness preserved. Therefore ATP availability uncoupled from bilayer dimensions unlike compositional factors distinguishing metabolic state structural parameter relevant membrane protein reconstitution crystallization and understanding mismatch sensing by Mga2 and Ire1 stress sensors in ER quality control pathways and unfolded protein response signaling.

Ref: Sharpe et al., Annu Rev Biophysics 2010, Hydrophobic mismatch thickness and proteins.

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Properties of Plasma Membrane

Which of the following lipids contributes to membrane thickness?

Membrane thickness determined by fatty acyl chain length unsaturation and sterol content influencing hydrophobic matching with integral protein transmembrane domains. Cholesterol small amphipathic sterol twenty seven carbons rigid tetracyclic ring structure with hydroxyl head and iso-octyl tail approximately one point five nanometer length intercalates among phospholipid acyl chains hydroxyl near glycerol carbonyl ester oxygen forming hydrogen bond, rigid rings restricting chain trans-gauche isomerization increasing order parameter measured by deuterium NMR and electron spin resonance, condensing average area per lipid from about zero point sixty to zero point fifty square nanometers and increasing hydrophobic thickness about zero point three to zero point five nanometers demonstrated by X-ray diffraction lamellar repeat. Sphingomyelin saturated long chains also increases thickness but cholesterol present up to fifty mole percent exerts pronounced thickening particularly in liquid-ordered raft domains enriched sphingomyelin cholesterol thicker than surrounding liquid-disordered phase containing unsaturated phosphatidylcholine. Proteins with longer transmembrane helices partition preferentially into thicker domains. Among listed lipids cholesterol therefore most directly modulates thickness and rigidity affecting Na K ATPase function and mechanosensitive channels.

Ref: de Meyer and Smit, Cholesterol Effect on Bilayer Thickness and Order, PNAS 2009.

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