Oiki S, Muramatsu I, Matsunaga S, Fusetani N
National Institute for Physiological Sciences, Aichi, Japan.
Nihon Yakurigaku Zasshi. 1997 Oct;110 Suppl 1:195P-198P. doi: 10.1254/fpj.110.supplement_195.
A highly cytotoxic extract from marine sponge, polytheonamide B, is a linear 48-residue peptide. Alternative D- and L-forms of unusual amino acids suggest formation of beta-helix that is stable in membrane and serves for ion conducting pore. The NMR study indicated that polytheonamide B forms beta-helix in methanol/chloroform solution. Channel activity of polytheonamide B was examined using planar lipid bilayers. Ionic current appeared from pM concentration. Measurements of the reversal potentials revealed that the channel showed cation selectivity. Single channel current was recorded in symmetrical 1 M solutions. The selectivity sequence was: H+ > Cs+ > Rb+ > K+ > Na+. Single-channel I-V curve exhibited slight inward rectification. Voltage-dependent transitions between brief openings and long closures were observed. Orientation of the peptide in the membrane was fixed when the peptide was added to one side of the chamber. The asymmetric behaviors, such as single channel rectification, voltage-dependent gating and oriented incorporation into the membrane, must be correlated to the molecular structure of polytheonamide B.
一种来自海洋海绵的具有高细胞毒性的提取物——聚醚酰胺B，是一种由48个残基组成的线性肽。其不同寻常的氨基酸的D型和L型交替排列，表明其形成了在膜中稳定且用于离子传导孔的β-螺旋结构。核磁共振研究表明，聚醚酰胺B在甲醇/氯仿溶液中形成β-螺旋结构。使用平面脂质双分子层检测了聚醚酰胺B的通道活性。离子电流在皮摩尔浓度时出现。对反转电位的测量表明，该通道具有阳离子选择性。在对称的1M溶液中记录了单通道电流。选择性顺序为：H⁺>Cs⁺>Rb⁺>K⁺>Na⁺。单通道电流-电压曲线表现出轻微的内向整流。观察到了短暂开放和长时间关闭之间的电压依赖性转变。当将肽添加到腔室的一侧时，肽在膜中的取向就固定了。诸如单通道整流、电压依赖性门控以及定向插入膜等不对称行为，必定与聚醚酰胺B的分子结构相关。
