| Research Abstract |
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
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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
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