title: ATP-independent reversal of a membrane protein aggregate by a chloroplast SRP subunit.
abstract: Membrane proteins impose enormous challenges to cellular protein homeostasis during their post-translational targeting, and they require chaperones to keep them soluble and translocation competent. Here we show that a novel targeting factor in the chloroplast signal recognition particle (cpSRP), cpSRP43, is a highly specific molecular chaperone that efficiently reverses the aggregation of its substrate proteins. In contrast to 'ATPases associated with various cellular activities' (AAA(+)) chaperones, cpSRP43 uses specific binding interactions with its substrate to mediate its 'disaggregase' activity. This disaggregase capability can allow targeting machineries to more effectively capture their protein substrates and emphasizes a close connection between protein folding and trafficking processes. Moreover, cpSRP43 provides the first example to our knowledge of an ATP-independent disaggregase and shows that efficient reversal of protein aggregation can be attained by specific binding interactions between a chaperone and its substrate.
authors.affiliation: Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California, USA.
authors.forename: Peera
authors.initials: P
authors.lastname: Jaru-Ampornpan
authors.forename: Kuang
authors.initials: K
authors.lastname: Shen
authors.forename: Vinh Q
authors.initials: VQ
authors.lastname: Lam
authors.forename: Mona
authors.initials: M
authors.lastname: Ali
authors.forename: Sebastian
authors.initials: S
authors.lastname: Doniach
authors.forename: Tony Z
authors.initials: TZ
authors.lastname: Jia
authors.forename: Shu-Ou
authors.initials: SO
authors.lastname: Shan
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D002736:Chloroplasts / Q000378:metabolism*; D007700:Kinetics; D045342:Light-Harvesting Protein Complexes / Q000737:chemistry / Q000378:metabolism; D008565:Membrane Proteins / Q000737:chemistry / Q000378:metabolism*; D008954:Models, Biological; D008958:Models, Molecular; D018832:Molecular Chaperones / Q000737:chemistry / Q000378:metabolism; D046912:Multiprotein Complexes; D011485:Protein Binding; D055503:Protein Multimerization; D021122:Protein Subunits; D021381:Protein Transport; D053838:Scattering, Small Angle; D018271:Signal Recognition Particle / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D014961:X-Ray Diffraction
chemical_list: D045342:Light-Harvesting Protein Complexes; D008565:Membrane Proteins; D018832:Molecular Chaperones; D046912:Multiprotein Complexes; D021122:Protein Subunits; D018271:Signal Recognition Particle; D000255:Adenosine Triphosphate