Braun V, Focareta T
Department of Microbiology, University of Tübingen, Germany.
Crit Rev Microbiol. 1991;18(2):115-58. doi: 10.3109/10408419109113511.
Protein toxins forming pores in biological membranes occur frequently in Gram-positive and Gram-negative bacteria. They kill either bacteria or eukaryotic cells (at most, a few seem to act on both groups of organisms). Most of the toxins affecting eukaryotes have clearly been shown to be related to the pathogenicity of the producing organisms. Toxin formation frequently involves a number of genes which encode the toxin polypeptide as well as proteins for toxin activation and secretion. Regulation of toxin production is usually coupled with that of the synthesis of a number of other virulence factors. Iron is the only known environmental factor that regulates transcription of a number of toxin genes by a Fur repressor-type mechanism, as has been originally described in Escherichia coli. Interestingly, the thiol-activated hemolysins (cytolysins) of Gram-positive bacteria contain a single cysteine which can be replaced by alanine without affecting the cytolytic activity. The Gram-negative hemolysins (cytolysins) are usually synthesized as precursor proteins, then covalently modified to yield an active hemolysin and secreted via specific export systems, which differ for various types of hemolysins.
在生物膜上形成孔道的蛋白质毒素在革兰氏阳性菌和革兰氏阴性菌中频繁出现。它们要么杀死细菌，要么杀死真核细胞（最多只有少数似乎对两类生物体都起作用）。大多数影响真核生物的毒素已被明确证明与产生毒素的生物体的致病性有关。毒素的形成通常涉及多个基因，这些基因编码毒素多肽以及用于毒素激活和分泌的蛋白质。毒素产生的调控通常与许多其他毒力因子的合成调控相关联。铁是唯一已知的通过Fur阻遏物型机制调节许多毒素基因转录的环境因子，这最初是在大肠杆菌中描述的。有趣的是，革兰氏阳性菌的硫醇激活溶血素（细胞溶素）含有一个半胱氨酸，该半胱氨酸可被丙氨酸替代而不影响细胞溶解活性。革兰氏阴性溶血素（细胞溶素）通常以前体蛋白的形式合成，然后进行共价修饰以产生活性溶血素，并通过特定的输出系统分泌，不同类型的溶血素其输出系统也不同。
