Solid-state NMR and SAXS studies provide a structural basis for the activation of αB-crystallin oligomers

• DOI: 10.1038/nsmb.1891
• Publication Date: 2010-08-29T17:28:35Z
• Authors: Stefan Jehle; Ponni Rajagopal; Benjamin Bardiaux; Stefan Markovic; Ronald Kühne; Joseph R Stout; Victoria A Higman; Rachel E Klevit; Barth-Jan van Rossum; Hartmut Oschkinat
• Keywords: CHAPERONE; info:eu-repo/classification/ddc/570; Models, Molecular; 570; 0303 health sciences; SPECTROSCOPY; Binding Sites; CRYSTALLOGRAPHY; ASSEMBLIES; alpha-Crystallin B Chain; UCSF CHIMERA; HEAT-SHOCK-PROTEIN; Hydrogen-Ion Concentration; 540; alpha-Crystallin B Chain: chemistry; Chemistry Techniques, Analytical; 03 medical and health sciences; AMYLOID FIBRILS; DOMAIN; X-RAY SOLUTION; Humans; Protein Structure, Quaternary; Nuclear Magnetic Resonance, Biomolecular; SOLUTION SCATTERING

The small heat shock protein alphaB-crystallin (alphaB) contributes to cellular protection against stress. For decades, high-resolution structural studies on oligomeric alphaB have been confounded by its polydisperse nature. Here, we present a structural basis of oligomer assembly and activation of the chaperone using solid-state NMR and small-angle X-ray scattering (SAXS). The basic building block is a curved dimer, with an angle of approximately 121 degrees between the planes of the beta-sandwich formed by alpha-crystallin domains. The highly conserved IXI motif covers a substrate binding site at pH 7.5. We observe a pH-dependent modulation of the interaction of the IXI motif with beta4 and beta8, consistent with a pH-dependent regulation of the chaperone function. N-terminal region residues Ser59-Trp60-Phe61 are involved in intermolecular interaction with beta3. Intermolecular restraints from NMR and volumetric restraints from SAXS were combined to calculate a model of a 24-subunit alphaB oligomer with tetrahedral symmetry.