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首页> 外文期刊>Journal of Molecular Biology >STRUCTURAL MODEL OF THE PHOSPHOLAMBAN ION CHANNEL COMPLEX IN PHOSPHOLIPID MEMBRANES
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STRUCTURAL MODEL OF THE PHOSPHOLAMBAN ION CHANNEL COMPLEX IN PHOSPHOLIPID MEMBRANES

机译：磷脂膜中磷脂离子通道复合物的结构模型

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摘要

Phospholamban is a 52 amino acid residue membrane protein involved with the regulation of calcium levels across sarcoplasmic reticulum membranes in cardiac muscle cells. The N-terminal 30 amino acid residues of the protein are largely hydrophilic and include two sites whose phosphorylation is thought to dissociate an inhibitory complex between phospholamban and Ca2+ ATPase. The C-terminal 22 amino acid residues are largely hydrophobic, anchor the protein in the membrane and are responsible for Ca2+ selective ion conductance. Specific interactions between the transmembrane domains stabilize a pentameric protein complex. We have obtained circular dichroism (CD), transmission Fourier transform infrared (FTIR) and attenuated total reflection Fourier transform infrared (ATR-FTIR) spectra of the full-length protein and have compared these results to those from a 28 residue peptide that includes the transmembrane domain. Both proteins reconstituted into phospholipid membranes are largely alpha-helical by CD and FTIR. Polarized ATR-FTIR measurements show that both the cytosolic and transmembrane helices are oriented perpendicular to the membrane plane with a tilt of 28 (+/-6)degrees with respect to the membrane normal. This tilt angle is in close agreement to that calculated from a model for the transmembrane domain of phospholamban suggested by mutagenesis and molecular modeling. Phosphorylation does not significantly change the secondary structure or orientation of the protein. The pentameric complex is modeled as a left-handed coiled-coil of five long helices (40 (+/-3) residues) that extended across the membrane from the lumenal carboxy terminus to the phosphorylation site in the cytoplasm. The helix bundle forms a perpendicular ion pore that may begin at a distance (17 to 29 Angstrom) from the membrane surface. Based on the above, we propose a mechanism by which phospholamban regulates Ca2+ levels across membranes that takes into account both its selective ion conductance and inhibitory association with the Ca2+ pump. [References: 44]
机译：Phospholamban是一种52个氨基酸残基的膜蛋白，参与调节心肌细胞中肌浆网膜的钙水平。该蛋白质的N端30个氨基酸残基在很大程度上是亲水性的，包括两个位点，其磷酸化被认为可解离磷酸lamban和Ca2 + ATPase之间的抑制复合物。 C末端的22个氨基酸残基在很大程度上疏水，将蛋白质锚定在膜中，并负责Ca2 +选择性离子电导。跨膜结构域之间的特定相互作用可稳定五聚体蛋白复合物。我们已经获得了全长蛋白的圆二色性（CD），透射傅立叶变换红外（FTIR）和衰减全反射傅立叶变换红外（ATR-FTIR）光谱，并将这些结果与包含28个残基的肽的结果进行了比较。跨膜结构域。 CD和FTIR两种重构为磷脂膜的蛋白质在很大程度上都是α螺旋。极化的ATR-FTIR测量结果表明，胞质和跨膜螺旋都垂直于膜平面定向，相对于膜法线倾斜28（+/- 6）度。该倾斜角与通过诱变和分子建模所暗示的从磷酸lamban的跨膜结构域的模型计算出的倾斜角非常一致。磷酸化不会显着改变蛋白质的二级结构或方向。五聚体复合物建模为五个长螺旋（40（+/- 3）个残基）的左旋卷曲螺旋，其从内腔羧基末端跨膜延伸至细胞质中的磷酸化位点。螺旋束形成垂直的离子孔，该离子孔可以在距膜表面一定距离（17到29埃）处开始。基于上述，我们提出了一种机制，磷酰胺可调节跨膜的Ca2 +水平，同时考虑到其选择性离子传导和与Ca2 +泵的抑制性缔合。 [参考：44]

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