title: Alternative bacterial two-component small heat shock protein systems.
abstract: Small heat shock proteins (sHsps) are molecular chaperones that prevent the aggregation of nonnative proteins. The sHsps investigated to date mostly form large, oligomeric complexes. The typical bacterial scenario seemed to be a two-component sHsps system of two homologous sHsps, such as the Escherichia coli sHsps IbpA and IbpB. With a view to expand our knowledge on bacterial sHsps, we analyzed the sHsp system of the bacterium Deinococcus radiodurans, which is resistant against various stress conditions. D. radiodurans encodes two sHsps, termed Hsp17.7 and Hsp20.2. Surprisingly, Hsp17.7 forms only chaperone active dimers, although its crystal structure reveals the typical α-crystallin fold. In contrast, Hsp20.2 is predominantly a 36mer that dissociates into smaller oligomeric assemblies that bind substrate proteins stably. Whereas Hsp20.2 cooperates with the ATP-dependent bacterial chaperones in their refolding, Hsp17.7 keeps substrates in a refolding-competent state by transient interactions. In summary, we show that these two sHsps are strikingly different in their quaternary structures and chaperone properties, defining a second type of bacterial two-component sHsp system.
authors.affiliation: Department of Chemistry, Center for Integrated Protein Science,  Technische Universität München, D-85748 Garching,  Germany.
authors.forename: Alexander
authors.initials: A
authors.lastname: Bepperling
authors.forename: Ferdinand
authors.initials: F
authors.lastname: Alte
authors.forename: Thomas
authors.initials: T
authors.lastname: Kriehuber
authors.forename: Nathalie
authors.initials: N
authors.lastname: Braun
authors.forename: Sevil
authors.initials: S
authors.lastname: Weinkauf
authors.forename: Michael
authors.initials: M
authors.lastname: Groll
authors.forename: Martin
authors.initials: M
authors.lastname: Haslbeck
authors.forename: Johannes
authors.initials: J
authors.lastname: Buchner
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure; D018360:Crystallography, X-Ray; D034301:Deinococcus / Q000235:genetics / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D050888:Heat-Shock Proteins, Small / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure; D046529:Microscopy, Electron, Transmission; D008958:Models, Molecular; D018832:Molecular Chaperones / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D017510:Protein Folding; D055503:Protein Multimerization; D020836:Protein Structure, Quaternary; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism / Q000648:ultrastructure; D017386:Sequence Homology, Amino Acid; D013312:Stress, Physiological
chemical_list: D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D050888:Heat-Shock Proteins, Small; D018832:Molecular Chaperones; D011994:Recombinant Proteins