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

以模型肽P24为跨膜a-螺旋肽及其4种类似物，研究了肽-肽带电相互作用和脂相分离在脂质双层螺旋-螺旋结合中的作用。将荧光氨基酸色氨酸（P24W）和芘丙氨酸（P24Pya）分别引入到P24序列中。这些肽的结合允许P24W中的色氨酸和P24Pya中的芘丙氨酸之间的共振激发能量传递或P24Pya本身之间的准分子形成。为了评价带电荷相互作用对膜蛋白A -螺旋跨膜段A之间结合的影响，分别在P24W和P24Pya中引入了带电荷氨基酸谷氨酸（P24EW）和赖氨酸（P24Kpya）。能量传递实验表明，P24KPya中赖氨酸残基的正电荷与P24EW中谷氨酸残基的负电荷之间的带电相互作用不影响脂质膜中跨膜肽的聚集。随着卵磷脂中鞘磷脂和胆固醇含量比例的增加，观察到P24Pya的准分子荧光光谱变强，表明卵磷脂脂质体中SM和Ch的共存，即SM和Ch的大量存在，促进了脂质双层中a-螺旋跨膜肽的聚集。由于SM和Ch含量的增加导致液晶有序相含量的减少，跨膜肽在脂质体中的移动面积可能受到限制，导致在脂筏存在下容易形成准分子

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