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Electrostatic and hydrophobic contributions to the folding mechanism of apocytochrome c driven by the interaction with lipid

机译：与脂质相互作用驱动载脂蛋白C折叠机制的静电和疏水作用

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In aqueous solution, while cytochrome c is a stably folded protein with a tightly packed structure at the secondary and tertiary levels, its heme-free precursor, apocytochrome c, shows all features of a structureless random coil. However, upon interaction with phospholipid vesicles or lysophospholipid micelles, apocytochrome c undergoes a conformational transition from its random coil in solution to an alpha-helical structure on association with lipid. The driving forces of this lipid-induced folding process of apocytochrome c were investigated for the interaction with various phospholipids and lysophospholipids. Binding of apocytochrome c to negatively charged phospholipid vesicles induced a partially folded state with similar to 85% of the alpha-helical structure of cytochrome c in solution. In contrast, in the presence of zwitterionic phospholipid vesicles, apocytochrome c remains a random coil, suggesting that negatively charged phospholipid headgroups play an important role in the mechanism of lipid-induced folding of apocytochrome c. However, negatively charged lysophospholipid micelles induce a higher content of alpha-helical structure than equivalent negatively charged diacylphospholipids in bilayers, reaching 100% of the alpha-helix content of cytochrome c in solution. Furthermore, micelles of lysolipids with the same zwitterionic headgroup of phospholipid bilayer vesicles induce similar to 60% of the alpha-helix content of cytochrome c in solution. On the basis of these results, we propose a mechanism for the folding of apocytochrome c induced by the interaction with lipid, which accounts for both electrostatic and hydrophobic contributions. Electrostatic lipid-protein interactions appear to direct the polypeptide to the micelle or vesicle surface and to induce an early partially folded state on the membrane surface. Hydrophobic interactions between nonpolar residues in the protein and the hydrophobic core of the lipid bilayer stabilize and extend the secondary structure upon membrane insertion. [References: 47]
机译：在水溶液中，细胞色素c是稳定折叠的蛋白质，在二级和三级具有紧密堆积的结构，而其不含血红素的前体脱细胞色素c则显示出无结构随机卷曲的所有特征。然而，在与磷脂囊泡或溶血磷脂微团相互作用时，脱细胞色素c从其溶液中的无规卷曲到与脂质缔合的α-螺旋结构发生构象转变。研究了这种脂质诱导的载脂细胞色素c折叠过程的驱动力，用于与各种磷脂和溶血磷脂的相互作用。脱辅基细胞色素c与带负电荷的磷脂囊泡的结合诱导了部分折叠状态，其溶液中细胞色素c的α-螺旋结构的含量约为85％。相反，在两性离子磷脂囊泡的存在下，载脂细胞色素c仍然是无规卷曲，这表明带负电荷的磷脂头基在脂质诱导的载脂细胞色素c折叠机制中起重要作用。但是，带负电荷的溶血磷脂胶束比双层中等效的带负电荷的二酰基磷酸脂诱导更高的α-螺旋结构含量，达到溶液中细胞色素c的α-螺旋含量的100％。此外，具有相同的两性离子磷脂双层囊泡的溶血脂的胶束可诱导溶液中细胞色素c的α-螺旋含量接近60％。基于这些结果，我们提出了一种通过与脂质相互作用而诱导的脱辅基细胞色素c折叠的机制，该机制解释了静电和疏水作用。静电脂质-蛋白质相互作用似乎将多肽引导至胶束或囊泡表面，并在膜表面诱导早期的部分折叠状态。蛋白质中非极性残基与脂质双层的疏水核心之间的疏水相互作用可在插入膜后稳定并扩展二级结构。 [参考：47]

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