Mechanism of Homotropic Control to Coordinate Hydrolysis in a Hexameric AAA+ Ring ATPase

Division of Biology, Imperial College London, London SW7 2AZ, UK.
Journal of Molecular Biology (Impact Factor: 4.33). 09/2008; 381(1):1-12. DOI: 10.1016/j.jmb.2008.05.075
Source: PubMed

ABSTRACT AAA(+) proteins are ubiquitous mechanochemical ATPases that use energy from ATP hydrolysis to remodel their versatile substrates. The AAA(+) characteristic hexameric ring assemblies raise important questions about if and how six often identical subunits coordinate hydrolysis and associated motions. The PspF AAA(+) domain, PspF(1-275), remodels the bacterial sigma(54)-RNA polymerase to activate transcription. Analysis of ATP substrate inhibition kinetics on ATP hydrolysis in hexameric PspF(1-275) indicates negative homotropic effects between subunits. Functional determinants required for allosteric control identify: (i) an important link between the ATP bound ribose moiety and the SensorII motif that would allow nucleotide-dependent *-helical */beta subdomain dynamics; and (ii) establishes a novel regulatory role for the SensorII helix in PspF, which may apply to other AAA(+) proteins. Consistent with functional data, homotropic control appears to depend on nucleotide state-dependent subdomain angles imposing dynamic symmetry constraints in the AAA(+) ring. Homotropic coordination is functionally important to remodel the sigma(54) promoter. We propose a structural symmetry-based model for homotropic control in the AAA(+) characteristic ring architecture.

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Available from: Nicolas Joly, Sep 27, 2015
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    • "The crystal structure of mutated, linked ClpX also shows a similar dimer of trimers structure (Glynn et al., 2009). Though similar nucleotide exchange reactions have been suggested by others (Hersch et al., 2005; Schumacher et al., 2008; Singleton et al., 2000), albeit without evidence of distinct functional consequences, the crystal structures of some AAA ATPases (e.g., HslU [Bochtler et al., 2000; Sousa et al., 2000; Yakamavich et al., 2008]) revealed seemingly promiscuous binding patterns for ATP analogs or ADP. An unambiguous elucidation of the binding exchange reactions for those ATPases has proven difficult because the number of nucleotides bound per hexamer has rarely been determined to a definite integer value (i.e., prior results could not distinguish between three or four nucleotides per hexamer). "
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    ABSTRACT: In the eukaryotic 26S proteasome, the 20S particle is regulated by six AAA ATPase subunits and, in archaea, by a homologous ring complex, PAN. To clarify the role of ATP in proteolysis, we studied how nucleotides bind to PAN. Although PAN has six identical subunits, it binds ATPs in pairs, and its subunits exhibit three conformational states with high, low, or no affinity for ATP. When PAN binds two ATPγS molecules or two ATPγS plus two ADP molecules, it is maximally active in binding protein substrates, associating with the 20S particle, and promoting 20S gate opening. However, binding of four ATPγS molecules reduces these functions. The 26S proteasome shows similar nucleotide dependence. These findings imply an ordered cyclical mechanism in which two ATPase subunits bind ATP simultaneously and dock into the 20S. These results can explain how these hexameric ATPases interact with and "wobble" on top of the heptameric 20S proteasome.
    Cell 02/2011; 144(4):526-38. DOI:10.1016/j.cell.2011.02.005 · 32.24 Impact Factor
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    • "In bEBPs the ATP hydrolysis site is configured through interactions between adjacent AAA+ protomers in the hexameric ring (Schumacher et al., 2008). Since the GAFTGA motif relays nucleotide-dependent interactions at this site to enable contact with s 54 , we were interested to examine if the G266 substitutions influence ATPase activity. "
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