Braun V, Ondraczek R, Hobbie S
Mikrobiologie II, Universität Tübingen, Germany.
Zentralbl Bakteriol. 1993 Apr;278(2-3):306-15. doi: 10.1016/s0934-8840(11)80847-9.
The hemolysin of Serratia marcescens (ShlA) is secreted into the culture medium and forms small pores of a defined size in erythrocytes and in black lipid membranes. The protein is synthesized as an inactive precursor of 1608 residues which is translocated across the cytoplasmic membrane by the Sec-export system. In the absence of the outer membrane protein ShlB, the ShlA protein (designated ShlA*) stays in the periplasm and displays about 0.1% of the activity of the secreted form. Secretion of ShlA with the help of ShlB is accompanied by its conversion to the hemolytic form. A ShlA derivative consisting of the N-terminal 238 residues of ShlA is secreted by ShlB, showing that the secretion signal resides in the amino terminal part of ShlA. ShlA* can be activated in vitro by a cell lysate containing ShlB, the activated ShlA remains hemolytic upon removal of ShlB. The assumed covalent modification of ShlA* by ShlB occurs in the N-terminus of ShlA since an amino terminal fragment (M(r) 28,000) secreted by ShlB, and a trypsin fragment of ShlA (M(r) 15,000) are both able to convert ShlA* to a hemolytic protein. In contrast to the permanent modification of ShlA* by ShlB, ShlA activity achieved by complementation with the ShlA fragments is abolished upon removal of the fragments. Apparently, the N-terminal portion of ShlA contains the information for secretion through the outer membrane and for insertion into the erythrocyte membrane. This information is lacking in ShlA* formed in the absence of ShlB but contained in the ShlA fragments formed in the presence of ShlB. The latter bind to ShlA* and direct ShlA* into the erythrocyte membrane. The fragments themselves are too short to build pores. The HpmA hemolysin of Proteus mirabilis shows extensive homology to ShlA. In vitro activation of HpmA* by ShlB and complementation by the 28 kDa ShlA fragment indicates a common activation mechanism.
粘质沙雷氏菌溶血素（ShlA）分泌到培养基中，并在红细胞和黑色脂质膜中形成特定大小的小孔。该蛋白质作为1608个残基的无活性前体合成，通过Sec-输出系统转运穿过细胞质膜。在没有外膜蛋白ShlB的情况下，ShlA蛋白（称为ShlA*）滞留在周质中，其活性约为分泌形式的0.1%。在ShlB的帮助下ShlA的分泌伴随着其转化为溶血形式。由ShlA的N端238个残基组成的ShlA衍生物由ShlB分泌，表明分泌信号位于ShlA的氨基末端部分。ShlA可在含有ShlB的细胞裂解物中体外激活，去除ShlB后，激活的ShlA仍具有溶血活性。推测ShlB对ShlA的共价修饰发生在ShlA的N端，因为ShlB分泌的氨基末端片段（分子量28,000）和ShlA的胰蛋白酶片段（分子量15,000）都能够将ShlA转化为溶血蛋白。与ShlB对ShlA的永久性修饰不同，通过与ShlA片段互补实现的ShlA活性在去除片段后消失。显然，ShlA的N端部分包含通过外膜分泌并插入红细胞膜的信息。在没有ShlB的情况下形成的ShlA缺乏该信息，但在有ShlB的情况下形成的ShlA片段中包含该信息。后者与ShlA结合并将ShlA导向红细胞膜。这些片段本身太短，无法形成小孔。奇异变形杆菌的HpmA溶血素与ShlA具有广泛的同源性。ShlB对HpmA的体外激活以及28 kDa ShlA片段的互补表明存在共同的激活机制。
