Molecular Design and Structure-Function of Ion Transfer Peptides : Investigation of structural stabilizing factor, Trp and Functional Factor, Glu

肽形成α -螺旋结构，导致脂质膜中的电压依赖性离子通道。已经证实，含2-氨基异丁酸（Aib）肽倾向于在脂质双分子层中形成α -螺旋构象和电压依赖性通道。本研究设计了具有不同链长的两亲性螺旋型含aib肽Ac- (Aib-Lys-Aib-Ala) n- nh2 (n=1-5，分别命名为BKBA-4、8、12、16和20)，用于研究含aib螺旋基序在脂质双分子层中的聚集和跨膜取向。采用固相法合成多肽。缓冲液中BKBA-4和BKBA-8的CD光谱在200 nm处呈弱带，为非有序结构。具有较长肽链的BKBA-12、16和20肽的CD谱表现出典型的双最小带，具有α -螺旋的特征。肽的螺旋度随链长的增加而增加。特别是BKBA-16和bkba - 20几乎具有完整的a-螺旋结构（分别为77%和85%）。在TFE中，BKBA-12、16和20也显示出显著的a-螺旋含量。通过比较缓冲液和TFE中肽的CD光谱，发现TFE中208 nm处的波段明显增加。TFE中椭圆率从208 ~ 225 nm的反转可能反映了TFE从缓冲中的聚集态向单链螺旋态的转变。此外，α -螺旋结构在磷脂脂质体中增强。特别是BKBA-16和bkba - 20的CD特征与alamethicin非常接近。这些结果表明BKBA-16和bkba - 20可能在磷脂双分子层中聚集并形成类似alamethicas的桶状壁构象。这种结构也可以通过使用膜片钳方法在双胆管中形成稳定的导电孔来证实。

Peptaibols form alpha-helical structures leading to voltage-dependent ion channels in lipid membranes. It has been confirmed that 2-aminoisobutyric acid (Aib)-containing peptides tend to take alpha-helix conformations and form voltage-dependent channels in lipid bilayrs. In the present study, amphiphilic helical Aib-containing peptides with various chain lengths, Ac- (Aib-Lys-Aib-Ala) n-NH2 (n=1-5 ; named as BKBA-4,8,12,16 and 20, respectively) have been designed to investigate the aggregation and transmembrane orientation of Aib-containing helical motifs in lipid bilayrs.Peptide synthesis was carried out by a solid-phase method. CD spectra of BKBA-4 and BKBA-8 in the buffer exhibited a weak band at 200 nm, representative of non-ordered structure. CD spectra of peptides having longer peptide chains, BKBA-12,16 and 20, exhibit the typical double minimum bands, characteristic of alpha-helix. The helicities of the peptides increased with increasing of chain length. In particular, BKBA-16 and 20 took almost complete a-helical structures (77 and 85%, respectively). In TFE,BKBA-12,16 and 20 also displayd significant a-helical contents. From comparing the CD spectra of the peptides in the buffer and TFE,the band at 208 nm increases dramatically in TFE.The reversal of the ellipticity ratio of 208 to 225 nm in TFE may reflect the transition from an aggregated state in buffer to single stranded helices in TFE.Moreover, the alpha-helical structures were intensified in phospholipid liposomes. Especially, CD characteristics of BKBA-16 and 20 were very close to those of alamethicin. These results suggest that BKBA-16 and 20 may aggregate and form alamethicin-like barrel-stave conformations in phospholipid bilayrs. This structure can be also confirmed by the formation of stable conducting pores in bilays, using patch-clamp methodology.