Effect of membrane dynamics on affecting molecular behavior of trans-membrane a -helical peptides

以跨膜α-螺旋肽P24及其4个类似物为模型肽，研究了肽-肽电荷相互作用和脂相分离在脂双层螺旋-螺旋缔合中的作用。将荧光氨基酸色氨酸（P24 W）和芘基丙氨酸（P24 Pya）分别引入P24的序列中。这些肽的缔合允许P24 W中的色氨酸和P24 Pya中的芘基丙氨酸之间的共振激发能量转移或P24 Pya自身之间的激基缔合物形成。为了评价带电相互作用对膜蛋白中α-螺旋跨膜片段A之间缔合的影响，将带电氨基酸谷氨酸（P24 EW）和赖氨酸（P24 Kpya）分别引入P24 W和P24 Pya中。能量传递实验表明，P24 KPya中赖氨酸残基的正电荷与P24 EW中谷氨酸残基的负电荷之间的相互作用不影响跨膜肽在脂膜上的聚集。随着卵磷脂中鞘磷脂和胆固醇含量比例的增加，P24 Pya的激基缔合物荧光光谱增强，说明卵磷脂脂质体中SM和Ch的共存，即SM和Ch的筏，促进了α-螺旋跨膜肽在脂质双层中的聚集。由于SM和Ch含量的增加导致液晶有序相含量的减少，因此跨膜肽在脂质体中的移动区域可能受到限制，从而导致在脂筏存在下容易形成激基缔合物

The roles of peptide-peptide charged interaction and lipid phase separation in helix-helix association in lipid bilayers were investigated using a model peptide, P24, as a transmembrane a-helical peptide, and its four analogues. Fluorescence ammo acids, tryptophan (P24W) and pyrenylalanine (P24Pya), were introduced into the sequence of P24, respectively. Association of these peptides permits the resonance excitation energy transfer between tryptophan in P24W and pyrenylalanine in P24Pya or excimer formation between P24Pya themselves. To evaluate the effect of charged interaction on the association between a-helical transmembrane segments A in membrane proteins, charged amino acids, glutamic acid (P24EW) and lysine (P24Kpya), were introduced into P24W and P24Pya, respectively. Energy transfer experiments indicated that the charged interaction between the positive charge of lysine residue in P24KPya and the negative charge of glutamic acid residue in P24EW did not affect the aggregation of transmembrane peptides in lipid membranes. As the content ratio of sphingomyelm and cholesterol was increased in the egg PC, the stronger excimer fluorescence spectra of P24Pya were observed, indicating that the co-existence of SM and Ch in PC liposomes, that is, the raft of SM and Ch, promotes the aggregation of thef a-helical transmembrane peptides in lipid bilayers. Since the increase in the contents of SM and Ch leads to the decrease in the content of liquid crystalline order phase, the moving area of transmembrane peptides might be limited in the liposomes, resulting in easy formation of the excimer in the presence of the lipid-raft