Department of Biochemistry, University of Saskatchewan, Saskatoon, Saskatchewan, Canada.
J Pept Sci. 2012 Aug;18(8):519-26. doi: 10.1002/psc.2429. Epub 2012 Jul 3.
Peptide modifications that improve pharmacological properties are of considerable therapeutic importance. Here we consider the retro (R), inversed (D) and retro-inversed (RI) isomers of glucagon with respect to structure, stability, toxicity and biological activity. Biologically, RI-glucagon demonstrated comparable in vivo activity as L-glucagon with respect to magnitude and duration of blood sugar elevation following i.p. administration to mice. Structurally, the isomers were investigated through circular dichroism (CD) and nanopore analysis. CD demonstrated a conserved potential for formation of secondary structure, which was independent of the direction of the peptide (L vs R; D vs RI) as well as formation of symmetry-related structures for the chiral isomers (L vs D; R vs RI). CD, therefore, discriminated chiral but not directional isomers. Nanopore analysis, which depends on interaction of the peptides with chiral pores, discriminated all four isomers on the basis of unique signatures of bumping and translocation. Nanopore analysis offered greater opportunity than CD to discriminate the isomers although neither technique provided a definitive biomarker of biological activity. Functionally, the R and RI isomers resist proteolytic degradation and none of the isomers possess hemolytic activity or cellular toxicity. Collectively, this investigation highlights the potentials and limitations of CD and nanopore analysis for investigation of peptide isomers as well as offering insight into the structural criteria to mimic peptide biological activity. For this example, retro-inversion, through undefined contributions of increased stability and maintained biological activity, was best suited to mimic the biological activity of the parent peptide.
改善药理学性质的肽修饰具有相当重要的治疗意义。在这里，我们考虑了胰高血糖素的反（R）、反向（D）和反向反向（RI）异构体，涉及结构、稳定性、毒性和生物活性。从生物学角度来看，RI-胰高血糖素在腹腔注射给药后升高血糖的幅度和持续时间方面与 L-胰高血糖素具有相当的体内活性。在结构上，通过圆二色性（CD）和纳米孔分析研究了这些异构体。CD 表明存在形成二级结构的保守潜力，这与肽的方向（L 与 R；D 与 RI）无关，也与手性异构体的对称相关结构的形成无关（L 与 D；R 与 RI）。因此，CD 区分了手性异构体，但没有区分方向性异构体。纳米孔分析依赖于肽与手性孔的相互作用，可以根据独特的碰撞和易位特征区分所有四个异构体。虽然这两种技术都没有提供生物活性的明确生物标志物，但纳米孔分析比 CD 提供了更多区分异构体的机会。在功能上，R 和 RI 异构体抵抗蛋白水解降解，并且没有任何异构体具有溶血活性或细胞毒性。总的来说，这项研究强调了 CD 和纳米孔分析在研究肽异构体方面的潜力和局限性，并提供了关于模拟肽生物活性的结构标准的见解。对于这个例子，通过增加稳定性和维持生物活性的未定义贡献，反向反转最适合模拟母体肽的生物活性。
