A key hydrophobic patch identified in an AAA⁺ protein essential for its in trans inhibitory regulation.
J Mol Biol 2013;
425:2656-69. [PMID:
23659791 PMCID:
PMC3791423 DOI:
10.1016/j.jmb.2013.04.024]
[Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2013] [Revised: 04/11/2013] [Accepted: 04/20/2013] [Indexed: 11/22/2022]
Abstract
Bacterial enhancer binding proteins (bEBPs) are a subclass of the AAA+ (ATPases Associated with various cellular Activities) protein family. They are responsible for σ54-dependent transcription activation during infection and function under many stressful growth conditions. The majority of bEBPs are regulated in their formation of ring-shaped hexameric self-assemblies via an amino-terminal domain through its phosphorylation or ligand binding. In contrast, the Escherichia coli phage shock protein F (PspF) is negatively regulated in trans by phage shock protein A (PspA). Up to six PspA subunits suppress PspF hexamer action. Here, we present biochemical evidence that PspA engages across the side of a PspF hexameric ring. We identify three key binding determinants located in a surface-exposed ‘W56 loop’ of PspF, which form a tightly packed hydrophobic cluster, the ‘YLW’ patch. We demonstrate the profound impact of the PspF W56 loop residues on ATP hydrolysis, the σ54 binding loop 1, and the self-association interface. We infer from single-chain studies that for complete PspF inhibition to occur, more than three PspA subunits need to bind a PspF hexamer with at least two binding to adjacent PspF subunits. By structural modelling, we propose that PspA binds to PspF via its first two helical domains. After PspF binding-induced conformational changes, PspA may then share structural similarities with a bEBP regulatory domain.
What is the mechanism of in trans inhibition of oligomeric self-assemblies?
Inhibitor initially docks on the AAA+ domain at a hydrophobic patch.
Consequently, ATPase and self-association of the AAA+ domain are altered.
Inhibitor’s structure mimics the evolutionarily divergent in cis regulatory domain.
In trans inhibition of oligomeric AAA+ domains requires multiple contacts.
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