title: Multiple sequence signals direct recognition and degradation of protein substrates by the AAA+ protease HslUV.
abstract: Proteolysis is important for protein quality control and for the proper regulation of many intracellular processes in prokaryotes and eukaryotes. Discerning substrates from other cellular proteins is a key aspect of proteolytic function. The Escherichia coli HslUV protease is a member of a major family of ATP-dependent AAA+ degradation machines. HslU hexamers recognize and unfold native protein substrates and then translocate the polypeptide into the degradation chamber of the HslV peptidase. Although a wealth of structural information is available for this system, relatively little is known about mechanisms of substrate recognition. Here, we demonstrate that mutations in the unstructured N-terminal and C-terminal sequences of two model substrates alter HslUV recognition and degradation kinetics, including changes in V(max). By introducing N- or C-terminal sequences that serve as recognition sites for specific peptide-binding proteins, we show that blocking either terminus of the substrate interferes with HslUV degradation, with synergistic effects when both termini are obstructed. These results support a model in which one terminus of the substrate is tethered to the protease and the other terminus is engaged by the translocation/unfolding machinery in the HslU pore. Thus, degradation appears to consist of discrete steps, which involve the interaction of different terminal sequence signals in the substrate with different receptor sites in the HslUV protease.
authors.affiliation: Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
authors.forename: Shankar
authors.initials: S
authors.lastname: Sundar
authors.forename: Kathleen E
authors.initials: KE
authors.lastname: McGinness
authors.forename: Tania A
authors.initials: TA
authors.lastname: Baker
authors.forename: Robert T
authors.initials: RT
authors.lastname: Sauer
mesh_terms: D001665:Binding Sites; D049071:Endopeptidase Clp / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D016297:Mutagenesis, Site-Directed; D010957:Plasmids; D025941:Protein Interaction Mapping; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism*; D012097:Repressor Proteins / Q000378:metabolism*; D013379:Substrate Specificity; D054334:Viral Regulatory and Accessory Proteins / Q000378:metabolism*
chemical_list: C483566:ClpYQ protease, E coli; D029968:Escherichia coli Proteins; D011993:Recombinant Fusion Proteins; D012097:Repressor Proteins; D054334:Viral Regulatory and Accessory Proteins; C016649:phage repressor proteins; D049071:Endopeptidase Clp