Length-Dependent Formation of Transmembrane Pores by 310-Helical α-Aminoisobutyric Acid Foldamers

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• 作者：Jennifer E. Jones ; Vincent Diemer ; Catherine Adam ; James Raftery ; Rebecca E. Ruscoe ; Jason T. Sengel ; Mark I. Wallace ; Antoine Bader ; Scott L. Cockroft ; Jonathan Clayden ; Simon J. Webb
• 刊名：Journal of the American Chemical Society
• 出版年：2016
• 出版时间：January 20, 2016
• 年：2016
• 卷：138
• 期：2
• 页码：688-695
• 全文大小：548K
• ISSN：1520-5126

文摘

The synthetic biology toolbox lacks extendable and conformationally controllable yet easy-to-synthesize building blocks that are long enough to span membranes. To meet this need, an iterative synthesis of α-aminoisobutyric acid (Aib) oligomers was used to create a library of homologous rigid-rod 3₁₀-helical foldamers, which have incrementally increasing lengths and functionalizable N- and C-termini. This library was used to probe the inter-relationship of foldamer length, self-association strength, and ionophoric ability, which is poorly understood. Although foldamer self-association in nonpolar chloroform increased with length, with a ～14-fold increase in dimerization constant from Aib₆ to Aib₁₁, ionophoric activity in bilayers showed a stronger length dependence, with the observed rate constant for Aib₁₁ ～70-fold greater than that of Aib₆. The strongest ionophoric activity was observed for foldamers with >10 Aib residues, which have end-to-end distances greater than the hydrophobic width of the bilayers used (～2.8 nm); X-ray crystallography showed that Aib₁₁ is 2.93 nm long. These studies suggest that being long enough to span the membrane is more important for good ionophoric activity than strong self-association in the bilayer. Planar bilayer conductance measurements showed that Aib₁₁ and Aib₁₃, but not Aib₇, could form pores. This pore-forming behavior is strong evidence that Aib_m (m ≥ 10) building blocks can span bilayers.