Studies on the E. coli FtsH protein, which has a homologous domain with Sec18p in Yeast.

ftsH基因对大肠杆菌的细胞活力至关重要。我们已经证明，FtsH蛋白是一个70.7 KDa的完整细胞质膜蛋白，横跨膜两次，并且它具有一个大的细胞质羧基末端部分，假定具有atp结合域。同源性研究显示，-200个氨基酸结构域，包括假定的atp结合序列，与一个新的真核假定的atp酶家族成员的结构域高度同源，例如Sec18p、Paslp、CDC48p和TBP-1，它们分别在蛋白质转运途径、过氧酶体组装、细胞分裂周期和基因表达中起作用。每个细胞的平均FtsH分子数估计约为400个。温度敏感的ftsHl突变在42°C时减少了隔膜形成酶，青霉素结合蛋白3 （PBP3）的数量。在ftsHl突变体中，位于羧基末端的PBP3的翻译后加工明显迟缓。更多的证据表明，ftsHl细胞中PBP3加工的延迟是由于输出缓慢或前PBP3状态的改变。ftsHl突变也被发现引起细胞内β -内酰胺酶前体形式的显著积累。虽然GroE活性没有受到ftsHl突变的显著影响，但伴侣蛋白GroEL/ES的过量产生刺激了ftsHl细胞中PBP3和β -内酰胺酶的加工。在ftsH基因中分离出了一个突变，该突变允许PhoA片段在SecY-PhoA融合蛋白中大量输出，其中PhoA序列连接到SecY的最后一个细胞质结构域，并被鉴定为单个碱基的变化。ftsHl突变以及ftsH的截断和atp结合序列变体也引起类似的表型，后两者比野生型等位基因占优势。atp结合位点突变的表达导致了β -内酰胺酶和OmpA的显著输出缺陷。这些结果表明，FtsH蛋白是一种膜结合的伴侣蛋白，参与了一些包膜蛋白的定位过程（易位、折叠和/或组装）。少

The ftsH gene is essential for cell viability in Escherichia coli. We have shown that FtsH protein is an integral cytoplasmic membrane protein of 70.7 KDa spanning the membrane twice, and that it has a large cytoplasmic carboxy-terminal part with a putative ATP-binding domain. Homology search revealed that a -200-amino-acid domain, including the putative ATP-binding sequence, is highly homologous to the domain found in members of a novel, eukaryotic family of putative ATPases, e.g., Sec18p, Paslp, CDC48p, and TBP-1, which function in protein transport pathways, peroxisome assembly, cell division cycle, and gene expression, respectively. The average number of FtsH molecules per cell was estimated to be approximately 400.A temperature-sensitive ftsHl mutation reduces the amount of a septum-forming enzyme, penicillin-binding protein 3 (PBP3) at 42ﾟC. The post-translational processing of PBP3, at the carboxy-terminal part, is significantly retarded in the ftsHl mutant. Evidence suggested t … More hat the delay of PBP3 processing in the ftsHl cells was due to either slow export or an altered state of pre-PBP3. The ftsHl mutation was also found to cause a marked intracellular accumulation of the precursor form of beta-lactamase. Although the GroE activity was not significantly affected by the ftsHl mutation, overproduction of the chaperonins GroEL/ES stimulated the processing of both PBP3 and beta-lactamase in the ftsHl cells.A mutation that allowed significant export of the PhoA moiety of the SecY-PhoA fusion protein, in which PhoA sequence is attached to the last cytoplasmic domain of SecY, across the membrane was isolated and identified as a single base change in the ftsH gene. The ftsHl mutation as well as a truncated and an ATP-binding sequence variants of ftsH also caused similar phenotypes, the latter two being dominant over the wild type allele. The expression of the ATP-binding site mutation caused significant export defects of beta-lactamase and OmpA. These results suggest that the FtsH protein is a membrane-bound chaperone involved in the localization processes (translocation, folding, and/or assembly) of some envelope proteins. Less