Department of Biology, University of Maryland, College Park, MD 20842, USA.
Int J Mol Sci. 2023 Jul 14;24(14):11473. doi: 10.3390/ijms241411473.
The outer membrane of Gram-negative bacteria contains a variety of pore-forming structures collectively referred to as porins. Some of these are voltage dependent, but weakly so, closing at high voltages. Triplin, a novel bacterial pore-former, is a three-pore structure, highly voltage dependent, with a complex gating process. The three pores close sequentially: pore 1 at positive potentials, 2 at negative and 3 at positive. A positive domain containing 14 positive charges (the voltage sensor) translocates through the membrane during the closing process, and the translocation is proposed to take place by the domain entering the pore and thus blocking it, resulting in the closed conformation. This mechanism of pore closure is supported by kinetic measurements that show that in the closing process the voltage sensor travels through most of the transmembrane voltage before reaching the energy barrier. Voltage-dependent blockage of the pores by polyarginine, but not by a 500-fold higher concentrations of polylysine, is consistent with the model of pore closure, with the sensor consisting mainly of arginine residues, and with the presence, in each pore, of a complementary surface that serves as a binding site for the sensor.
革兰氏阴性细菌的外膜含有多种孔形成结构，统称为孔蛋白。其中一些是电压依赖性的，但依赖性较弱，在高电压下关闭。三孔蛋白是一种新型的细菌孔形成蛋白，具有三个孔，高度依赖电压，具有复杂的门控过程。三个孔依次关闭：正电位时关闭孔 1，负电位时关闭孔 2，正电位时关闭孔 3。一个包含 14 个正电荷的正域（电压传感器）在关闭过程中穿过膜，并且提出了通过域进入孔并因此阻塞它来发生的易位，导致封闭构象。这种孔关闭机制得到了动力学测量的支持，该测量表明在关闭过程中，电压传感器在到达能量障碍之前穿过大部分跨膜电压。多聚精氨酸对孔的电压依赖性阻断，而不是 500 倍更高浓度的多聚赖氨酸，与孔关闭模型一致，传感器主要由精氨酸残基组成，并且在每个孔中存在互补表面，作为传感器的结合位点。
