Membrane biophysical studies of the colicin E1 channel

大肠杆菌素是某些大肠杆菌菌株在细菌细胞生长过程中产生的有毒蛋白质，它们通常是在一系列代谢挑战下产生的，包括DNA损伤、厌氧症、分解代谢抑制和营养物质消耗。Colicin E1 （colE1）是通道形成colicins的成员，colicins还包括colicins a、B、Ia、Ib、N和K. colicins的三维结构揭示了colicins存在三个结构域：受体结合结构域、易位结构域和通道结构域。受体结合域通过与细菌外膜上的维生素B12受体结合，启动毒素进入靶细胞。接下来，易位结构域与三聚体ß-barrel TolC外膜受体结合，通过该受体，大肠杆菌素被转运到目标细菌的周质中。在一系列步骤中，colE1依次展开、结合并自发插入到膜中，形成封闭的通道状态。该通道在存在反负膜电位的情况下打开，并通过Na+， K+和H+等细胞离子的逃逸引起宿主细胞质膜的去极化。

Colicins are toxic proteins produced by certain strains of E. coli during bacterial cell growth and they are often produced in response to a host of metabolic challenges, including DNA damage, anaerobiosis, catabolite repression and nutrient depletion. Colicin E1 (colE1) is a member of the channel-forming colicins, which also includes colicins A, B, Ia, Ib, N and K. The three-dimensional structures of colicins reveal the presence of three domains: receptor binding, translocation and channel domains. The receptor-binding domain initiates toxin entry into target cells by binding with the vitamin B12 receptor on the bacterial outer membrane. Next, the translocation domain associates with the trimeric ß-barrel TolC outer membrane receptor, through which the colicin is transported into the periplasm of the target bacterium. In a series of steps, colE1 sequentially unfolds, binds and spontaneously inserts into the membrane to form a closed channel state. The channel opens in the presence of a trans-negative membrane potential and causes depolarization of the host cell cytoplasmic membrane through the escape of cellular ions such as Na+, K+ and H+.