From the common molecular basis of the AAA protein to various energy-dependent and -independent activities of AAA proteins

Abstract

AAA (ATPase associated with various cellular activities) proteins remodel substrate proteins and protein complexes upon ATP hydrolysis. Substrate remodelling is diverse, e.g. proteolysis, unfolding, disaggregation and disassembly. In the oligomeric ring of the AAA protein, there is a conserved aromatic residue which lines the central pore. Functional analysis indicates that this conserved residue in AAA proteases is involved in threading unfolded polypeptides. Katanin and spastin have microtubule-severing activity. These AAA proteins also possess a conserved aromatic residue at the central pore, suggesting its importance in their biological activity. We have constructed pore mutants of these AAA proteins and have obtained in vivo and in vitro results indicating the functional importance of the pore motif. Degradation of casein by the Escherichia coli AAA protease, FtsH, strictly requires ATP hydrolysis. We have constructed several chimaeric proteases by exchanging domains of FtsH and its homologues from Caenorhabditis elegans mitochondria, and examined their ATPase and protease activities in vitro. Interestingly, it has been found that some chimaeras are able to degrade casein in an ATP-independent manner. The proteolysis is supported by either ATP[S] (adenosine 5'-[gamma-thio]triphosphate) or ADP, as well as ATP. It is most likely that substrate translocation in these chimaeras occurs by facilitated diffusion. We have also investigated the roles of C. elegans p97 homologues in aggregation/disaggregation of polyglutamine repeats, and have found that p97 prevents filament formation of polyglutamine proteins in an ATP-independent fashion.

Distinct conformations of the protein complex p97-Ufd1-Npl4 revealed by electron cryomicroscopy

“…The role of the pore in the recruitment and extraction of substrates is still contentious. It has been shown that substrates interact with residues in the D2 pore on the distal side of the ring (31,32), and it has been suggested that they are not threaded down the central pore as proposed for other members of the AAA family (33)(34)(35)(36).…”

Dual Role of FtsH in Regulating Lipopolysaccharide Biosynthesis in Escherichia coli

“…Here we identify a new FtsH substrate-3-deoxy-D-manno-octulosonate (KDO) transferase-which carries out the attachment of two KDO residues to the lipid A precursor (lipid IV A ) to form the minimal essential structure of the lipopolysaccharide (LPS) (KDO 2 -lipid A). Thus, FtsH regulates the concentration of the lipid moiety of LPS (lipid A) as well as the sugar moiety (KDO-based core oligosaccharides), ensuring a balanced synthesis of LPS.FtsH (HflB) is an ATP-dependent, membrane-bound protease (17, 18) which belongs to the AAA family (ATPases associated with diverse cellular activities) (2,26,31,36). FtsH degrades proteins tagged with the SsrA degradation peptide (12, 13) as well as YccA, SecY, and the ATPase F 0 when they are not complexed (1,20).…”

“…FtsH (HflB) is an ATP-dependent, membrane-bound protease (17, 18) which belongs to the AAA family (ATPases associated with diverse cellular activities) (2,26,31,36). FtsH degrades proteins tagged with the SsrA degradation peptide (12, 13) as well as YccA, SecY, and the ATPase F 0 when they are not complexed (1,20).…”

AAA proteins and the life process

“…Abbreviations used: AAA, ATPase associated with various cellular activities; ER, endoplasmic reticulum; ERAD, ER-associated degradation; MCM, mini-chromosome maintenance; VCP, valosincontaining protein. 1 To whom correspondence should be addressed (email p.freemont@imperial.ac.uk). studies on the AAAs.…”