Macao B, Luirink J, Samuelsson T
Department of Medical Biochemistry, Göteborg University, Sweden.
Mol Microbiol. 1997 May;24(3):523-34. doi: 10.1046/j.1365-2958.1997.3551729.x.
Mycoplasma mycoides contains a signal-recognition particle (SRP) composed of an RNA molecule and an SRP54 homologue (Ffh). We have now identified a mycoplasma homologue to the alpha subunit of the mammalian SRP receptor and Escherichia coli FtsY. The protein (MmFtsY) was expressed in E. coli and purified to homogeneity. MmFtsY has a weak intrinsic GTPase activity but GTP hydrolysis was markedly stimulated when it was combined with mycoplasma Ffh (MmFfh) and SRP RNA. Also, in the absence of SRP RNA GTPase activity was significantly enhanced. Furthermore, GTP hydrolysis was stimulated when MmFtsY was combined with the N-terminal GTPase domain (N+G) of MmFfh. These findings indicate that basic features of the GTPase activation mechanism are independent of the C-terminal M domain of the MmFfh protein. We propose that the activation is mediated to a large extent by contacts between the GTPase domains of the mycoplasma Ffh and FtsY proteins and that the contribution of the M domain and SRP RNA in the activation mechanism is mainly for modifying the conformation of the MmFfh GTPase domain.
蕈状支原体含有一种由RNA分子和SRP54同源物（Ffh）组成的信号识别颗粒（SRP）。我们现已鉴定出一种与哺乳动物SRP受体的α亚基以及大肠杆菌FtsY同源的支原体蛋白。该蛋白（MmFtsY）在大肠杆菌中表达并纯化至同质。MmFtsY具有较弱的内在GTP酶活性，但当它与支原体Ffh（MmFfh）和SRP RNA结合时，GTP水解受到显著刺激。此外，在没有SRP RNA的情况下，GTP酶活性也显著增强。而且，当MmFtsY与MmFfh的N端GTP酶结构域（N + G）结合时，GTP水解也受到刺激。这些发现表明，GTP酶激活机制的基本特征与MmFfh蛋白的C端M结构域无关。我们提出，激活在很大程度上是由支原体Ffh和FtsY蛋白的GTP酶结构域之间的相互作用介导的，并且M结构域和SRP RNA在激活机制中的作用主要是改变MmFfh GTP酶结构域的构象。
