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The inherent heterogeneity of many protein assemblies complicates characterization of their structure and dynamics, as most biophysical techniques require homogeneous preparations of isolated components. For this reason, quantitative studies of the molecular chaperone αB-crystallin, which populates a range of interconverting oligomeric states, have been difficult, and the physicochemical basis for its polydispersity has remained unknown. Here, we perform mass spectrometry experiments to study αB-crystallin and extract detailed information as to its oligomeric distribution and exchange of subunits under a range of conditions. This allows a determination of the thermodynamic and kinetic parameters that govern the polydisperse ensemble and enables the construction of a simple energy profile for oligomerization. We find that the quaternary structure and dynamics of the protein can be explained using a simple model with just two oligomer-independent interactions (i.e., interactions that are energetically identical in all oligomers from 10mers to 40mers) between constituent monomers. As such, the distribution of oligomers is governed purely by the dynamics of individual monomers. This provides a new means for understanding the polydispersity of αB-crystallin and a framework for interrogating other heterogeneous protein assemblies.

Original publication

DOI

10.1016/j.jmb.2011.07.016

Type

Journal article

Journal

J Mol Biol

Publication Date

21/10/2011

Volume

413

Pages

297 - 309

Keywords

Escherichia coli, Hydrogen-Ion Concentration, Kinetics, Models, Molecular, Poisson Distribution, Protein Multimerization, Protein Structure, Quaternary, Protein Subunits, Spectrometry, Mass, Electrospray Ionization, Thermodynamics, alpha-Crystallin A Chain, alpha-Crystallin B Chain