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1000
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Abstract/Summary
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The small heat shock protein αB-crystallin (αB) contributes to cellular protection against stress. For decades, high-resolution structural studies on oligomeric αB 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 ∼121° between the planes of the β-sandwich formed by α-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 β4 and β8, consistent with a pH-dependent regulation of the chaperone function. N-terminal region residues Ser59-Trp60-Phe61 are involved in intermolecular interaction with β3. Intermolecular restraints from NMR and volumetric restraints from SAXS were combined to calculate a model of a 24-subunit αB oligomer with tetrahedral symmetry.
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