Cyclic homodetic peptides having a repeating D-L-chirality motif are shown to have a stable disk conformation with the amino acid side chains extending radially outward and the carbonyl and amino groups extending axially upward or downward. Such cyclic peptides can be employed as subunits in the assembly of molecular tubes. Cyclic peptides having a repeating D-L-chirality motif and lacking mutually repulsive side-chains are shown to stack atop one another in an anti-parallel fashion and are shown to be held together by the formation of &bgr;-sheet hydrogen bonding. The stacked cyclic peptides form a molecular tube having a central channel. The diameter of the channel is determined by the size cyclic peptide. If the cyclic peptide includes ionizable amino acid residues, e.g. glutamic acid or lysine, assembly and disassembly of the molecular tubes can be controlled by varying the pH. If the cyclic peptide includes hydrophobic amino acid residues, the molecular tube will insert into a lipid membrane. In such instances, the molecular tube provides a transmembrane channel. The channel can be gated or ungated. Molecular tubes can be terminated with a terminal cyclic peptide having methylated amino groups in one orientation. Molecular tubes may be employed as drug carriers, molecular sieves, reaction vessels, membrane channels, and other uses.
研究表明,具有重复 D-L 手性图案的环状同源肽具有稳定的圆盘构象,
氨基酸侧链沿径向向外延伸,羰基和
氨基沿轴向向上或向下延伸。这种环肽可用作组装分子管的亚单位。具有重复的 D-L 手性图案和缺乏互斥侧链的环肽以反平行方式相互堆叠,并通过形成&bgr;-sheet 氢键而固定在一起。堆叠的环肽形成了一个具有中央通道的分子管。通道的直径由环肽的大小决定。如果环肽包括可电离的
氨基酸残基,如谷
氨酸或赖
氨酸,则分子管的组装和拆卸可通过改变 pH 值来控制。如果环肽包括疏
水性
氨基酸残基,分子管就会插入脂膜。在这种情况下,分子管提供了一个跨膜通道。通道可以是门控的,也可以是非门控的。分子管的末端可以是环肽,环肽在一个方向上具有甲基化的
氨基。分子管可用作药物载体、
分子筛、反应容器、膜通道及其它用途。