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M. B. Dolinska, P. T. Wingfield, Y. V. Sergeev; Homo- and Hetero-Associations of βB1-Crystallin Are Dominated by Enthalpy. Invest. Ophthalmol. Vis. Sci. 2010;51(13):4613.
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© ARVO (1962-2015); The Authors (2016-present)
β-crystallins are structural proteins of the mammalian eye lens. Their homo- and hetero-associations play a significant role in processes related to lens transparency and opacification. Self-association of βB2 and βA3 crystallins into dimers is driven by entropy and involves hydrophobic interactions. It was recently shown that βB1 and βA3 form hetero-tetramers. To investigate driving force causing tetramerization, energetics of βB1 homo- and hetero-associations were studied.
Crystallins βB1 and βA3 were expressed in E.coli and purified from the soluble fractions using ion-exchange and size-exclusion chromatographies. Homo- and hetero-associations were characterized using sedimentation equilibrium measured at various temperatures from 5 to 30°C with 5°C increments.
Individual crystallins were reversible monomer-dimer systems over the temperature range studied. However, the dimerization potential of βB1, unlike βA3, is weakened with increased temperature. Tetramer formation between βB1 and βA3 was also destabilized by temperature increases. Associations in βB1 dimer and βA3/βB1 tetramer result in negative changes of Gibbs free energy, enthalpy and entropy. This indicates that βB1 homo- and hetero-associations are controlled by enthalpy change.
The enthalpy effect suggests that van der Waals contacts and hydrogen bonds are involved in protein-protein interactions within inter-subunit interface of βB1 homo-dimer and βB1/βA3 hetero-tetramer.
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