title: N-terminal domain of alphaB-crystallin provides a conformational switch for multimerization and structural heterogeneity.
abstract: The small heat shock protein (sHSP) αB-crystallin (αB) plays a key role in the cellular protection system against stress. For decades, high-resolution structural studies on heterogeneous sHSPs have been confounded by the polydisperse nature of αB oligomers. We present an atomic-level model of full-length αB as a symmetric 24-subunit multimer based on solid-state NMR, small-angle X-ray scattering (SAXS), and EM data. The model builds on our recently reported structure of the homodimeric α-crystallin domain (ACD) and C-terminal IXI motif in the context of the multimer. A hierarchy of interactions contributes to build multimers of varying sizes: Interactions between two ACDs define a dimer, three dimers connected by their C-terminal regions define a hexameric unit, and variable interactions involving the N-terminal region define higher-order multimers. Within a multimer, N-terminal regions exist in multiple environments, contributing to the heterogeneity observed by NMR. Analysis of SAXS data allows determination of a heterogeneity parameter for this type of system. A mechanism of multimerization into higher-order asymmetric oligomers via the addition of up to six dimeric units to a 24-mer is proposed. The proposed asymmetric multimers explain the homogeneous appearance of αB in negative-stain EM images and the known dynamic exchange of αB subunits. The model of αB provides a structural basis for understanding known disease-associated missense mutations and makes predictions concerning substrate binding and the reported fibrilogenesis of αB.
authors.affiliation: Department of Biochemistry, University of Washington, Seattle, WA 98195, USA.
authors.forename: Stefan
authors.initials: S
authors.lastname: Jehle
authors.forename: Breanna S
authors.initials: BS
authors.lastname: Vollmar
authors.forename: Benjamin
authors.initials: B
authors.lastname: Bardiaux
authors.forename: Katja K
authors.initials: KK
authors.lastname: Dove
authors.forename: Ponni
authors.initials: P
authors.lastname: Rajagopal
authors.forename: Tamir
authors.initials: T
authors.lastname: Gonen
authors.forename: Hartmut
authors.initials: H
authors.lastname: Oschkinat
authors.forename: Rachel E
authors.initials: RE
authors.lastname: Klevit
mesh_terms: D000818:Animals; D006801:Humans; D008958:Models, Molecular; D020125:Mutation, Missense; D019906:Nuclear Magnetic Resonance, Biomolecular; D055503:Protein Multimerization; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary; D038203:alpha-Crystallin B Chain / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism
chemical_list: D038203:alpha-Crystallin B Chain