Rasheed J K, Guzmán-Verduzco L M, Kupersztoch Y M
Department of Microbiology, University of Texas, Southwestern Medical Center, Dallas 75235.
Mol Microbiol. 1990 Feb;4(2):265-73. doi: 10.1111/j.1365-2958.1990.tb00593.x.
Expression of the gene of the methanol-soluble, heat-stable enterotoxin of Escherichia coli (STA) allowed the identification by SDS-PAGE of a cell-associated 7500 Dalton STA-related peptide; when similar experiments were performed with a phosphate buffer SDS-PAGE system, an additional Mr 9800 band became apparent. The 9800 Dalton form, pre-pro-STA, accumulated as an intracellular species when the experiments were performed in the presence of the proton ionophore CCCP (carbonylcyanide m-chlorophenylhydrazone); by pulse-chase experiments, it was shown that pre-pro-STA became a periplasmic Mr 7500 pro-STA and this form was chased to the culture supernatant; periplasmic and extracellular pro-STA showed the same electrophoretic mobility. A short time after the pulse, pro-STA was converted extracellularly to mature STA (Mr 4500). It is proposed that STA is synthesized as pre-pro-STA, a 72-amino-acid peptide that is subsequently cleaved between amino acids 19 and 20 as it is translocated across the inner membrane. The resulting 53-amino-acid pro-STA is first detected in the periplasm and is then secreted to the culture supernatant. Pro-STA is cleaved extracellularly to yield mature STA (Mr 4500).
大肠杆菌甲醇可溶、热稳定肠毒素（STA）基因的表达使得通过SDS-PAGE鉴定出一种与细胞相关的7500道尔顿STA相关肽；当用磷酸盐缓冲液SDS-PAGE系统进行类似实验时，一条额外的9800道尔顿条带变得明显。当在质子离子载体CCCP（羰基氰化物间氯苯腙）存在下进行实验时，9800道尔顿形式的前体STA作为一种细胞内物质积累；通过脉冲追踪实验表明，前体STA变成了周质中的7500道尔顿的pro-STA，并且这种形式被追踪到培养上清液中；周质和细胞外的pro-STA显示出相同的电泳迁移率。脉冲后短时间内，pro-STA在细胞外被转化为成熟的STA（4500道尔顿）。有人提出，STA以前体STA的形式合成，前体STA是一种72个氨基酸的肽，在其跨内膜转运时随后在第19和20个氨基酸之间被切割。产生的53个氨基酸的pro-STA首先在周质中被检测到，然后分泌到培养上清液中。pro-STA在细胞外被切割产生成熟的STA（4500道尔顿）。
