Laboratoire de Physique Statistique, Ecole Normale Supérieure, Université Paris Diderot, CNRS, 24 rue Lhomond, 75005 Paris, France.
J Phys Chem B. 2010 Mar 18;114(10):3559-66. doi: 10.1021/jp911354y.
A hydrophobic mismatch between protein length and membrane thickness can lead to a modification of protein conformation, function, and oligomerization. To study the role of hydrophobic mismatch, we have measured the change in mobility of transmembrane peptides possessing a hydrophobic helix of various length d(pi) in lipid membranes of giant vesicles. We also used a model system where the hydrophobic thickness of the bilayers, h, can be tuned at will. We precisely measured the diffusion coefficient of the embedded peptides and gained access to the apparent size of diffusing objects. For bilayers thinner than d(pi), the diffusion coefficient decreases, and the derived characteristic sizes are larger than the peptide radii. Previous studies suggest that peptides accommodate by tilting. This scenario was confirmed by ATR-FTIR spectroscopy. As the membrane thickness increases, the value of the diffusion coefficient increases to reach a maximum at h approximately = d(pi). We show that this variation in diffusion coefficient is consistent with a decrease in peptide tilt. To do so, we have derived a relation between the diffusion coefficient and the tilt angle, and we used this relation to derive the peptide tilt from our diffusion measurements. As the membrane thickness increases, the peptides raise (i.e., their tilt is reduced) and reach an upright position and a maximal mobility for h approximately = d(pi). Using accessibility measurements, we show that when the membrane becomes too thick, the peptide polar heads sink into the interfacial region. Surprisingly, this "pinching" behavior does not hinder the lateral diffusion of the transmembrane peptides. Ultimately, a break in the peptide transmembrane anchorage is observed and is revealed by a "jump" in the D values.
蛋白质长度与膜厚度之间的疏水失配会导致蛋白质构象、功能和寡聚化的改变。为了研究疏水失配的作用，我们测量了具有不同长度 d(pi)的疏水螺旋的跨膜肽在巨囊泡脂质膜中的迁移率变化。我们还使用了一个可以随意调节双层膜疏水厚度 h 的模型系统。我们精确测量了嵌入肽的扩散系数，并获得了扩散物体的表观大小。对于比 d(pi)薄的双层膜，扩散系数减小，得出的特征尺寸大于肽半径。先前的研究表明，肽通过倾斜来适应。ATR-FTIR 光谱学证实了这种情况。随着膜厚度的增加，扩散系数的值增加，在 h 约等于 d(pi)时达到最大值。我们表明，这种扩散系数的变化与肽倾斜的减少一致。为此，我们推导出了扩散系数与倾斜角之间的关系，并使用该关系从我们的扩散测量中推导出肽的倾斜角。随着膜厚度的增加，肽向上抬起（即倾斜减小），并在 h 约等于 d(pi)时达到直立位置和最大的流动性。通过可及性测量，我们表明当膜变得太厚时，肽的极性头部会沉入界面区域。令人惊讶的是，这种“挤压”行为不会阻碍跨膜肽的侧向扩散。最终，观察到肽跨膜锚固的中断，并通过 D 值的“跳跃”揭示出来。
