title: The ClpS adaptor mediates staged delivery of N-end rule substrates to the AAA+ ClpAP protease.
abstract: The ClpS adaptor delivers N-end rule substrates to ClpAP, an energy-dependent AAA+ protease, for degradation. How ClpS binds specific N-end residues is known in atomic detail and clarified here, but the delivery mechanism is poorly understood. We show that substrate binding is enhanced when ClpS binds hexameric ClpA. Reciprocally, N-end rule substrates increase ClpS affinity for ClpA(6). Enhanced binding requires the N-end residue and a peptide bond of the substrate, as well as multiple aspects of ClpS, including a side chain that contacts the substrate α-amino group and the flexible N-terminal extension (NTE). Finally, enhancement also needs the N domain and AAA+ rings of ClpA, connected by a long linker. The NTE can be engaged by the ClpA translocation pore, but ClpS resists unfolding/degradation. We propose a staged-delivery model that illustrates how intimate contacts between the substrate, adaptor, and protease reprogram specificity and coordinate handoff from the adaptor to the protease.
authors.affiliation: Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
authors.forename: Giselle
authors.initials: G
authors.lastname: Román-Hernández
authors.forename: Jennifer Y
authors.initials: JY
authors.lastname: Hou
authors.forename: Robert A
authors.initials: RA
authors.lastname: Grant
authors.forename: Robert T
authors.initials: RT
authors.lastname: Sauer
authors.forename: Tania A
authors.initials: TA
authors.lastname: Baker
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites; D002352:Carrier Proteins / Q000737:chemistry* / Q000378:metabolism; D018360:Crystallography, X-Ray; D049071:Endopeptidase Clp / Q000737:chemistry / Q000378:metabolism; D004926:Escherichia coli / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000378:metabolism; D008969:Molecular Sequence Data; D012680:Sensitivity and Specificity; D013379:Substrate Specificity
chemical_list: D002352:Carrier Proteins; C454820:ClpS protein, E coli; D029968:Escherichia coli Proteins; D049071:Endopeptidase Clp