Vasil M L, Kabat D, Iglewski B H
Infect Immun. 1977 Apr;16(1):353-61. doi: 10.1128/iai.16.1.353-361.1977.
The relation of the structure of Pseudomonas aeruginosa exotoxin A (PA toxin) to its enzymatic activity (adenosine 5'-diphosphate-ribosyl transferase) in vitro and to its toxicity in vivo was examined. PA toxin is produced as a single polypeptide chain with a molecular weight of about 71,500. PA toxin is produced by Pseudomonas as a toxic proenzyme that lacks enzymatic activity. Adenosine 5'-diphosphate-ribosyl transferase activity is expressed when the molecule is denatured and reduced or when its is cleaved by Pseudomonas proteases to yield an enzymatically active 27,000-dalton fragment (fragment a). A 45,000-dalton protein is tentatively identified as the enzymatically inactive fragment b of PA toxin. Enzymatically active forms of the toxin lack toxicity for mouse L-cells or mouse lethality. Thus, it is concluded that the native toxin proenzyme is required for toxicity and that a structural rearrangement must precede its intracellular activity.
研究了铜绿假单胞菌外毒素A（PA毒素）的结构与其体外酶活性（腺苷5'-二磷酸核糖基转移酶）及体内毒性之间的关系。PA毒素作为一种分子量约为71,500的单条多肽链产生。PA毒素由铜绿假单胞菌作为一种缺乏酶活性的毒性酶原产生。当分子变性并还原时，或者当它被铜绿假单胞菌蛋白酶切割产生一个具有酶活性的27,000道尔顿片段（片段a）时，腺苷5'-二磷酸核糖基转移酶活性得以表达。一个45,000道尔顿的蛋白质被初步鉴定为PA毒素的无酶活性片段b。该毒素的酶活性形式对小鼠L细胞无毒性或对小鼠无致死性。因此，可以得出结论，天然毒素酶原是毒性所必需的，并且在其细胞内活性之前必须有结构重排。
