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Abstract
Lens alpha-crystallin subunits alphaA and alphaB are differentially expressed and have a 3-to-1 ratio in most mammalian lenses by intermolecular exchange. The biological significance of this composition and the mechanism of exchange are not clear. Preparations of human recombinant alphaA- and alphaB-crystallins provide a good system in which to study this phenomenon. Both recombinant alphaA- and alphaB-crystallins are folded and aggregated to the size of the native alpha-crystallin. During incubation together, they undergo an intermolecular exchange as shown by native isoelectric focusing. Circular dichroism measurements indicate that the protein with a 3-to-1 ratio of alphaA- and alphaB-crystallins has the same secondary structure but somewhat different tertiary structures after exchange: the near-UV CD increases after exchange. The resulting hybrid aggregate is more stable than the individual homogeneous aggregates: at 62 degrees C, alphaB-crystallin is more susceptible to aggregation and displays a greater light scattering than alphaA-crystallin. This heat-induced aggregation of alphaB-crystallin, however, was suppressed by intermolecular exchange with alphaA-crystallin. These phenomena are also observed by fast performance liquid chromatography gel filtration patterns. The protein structure of alphaB-crystallin is stabilized by intermolecular exchange with alphaA-crystallin.
Highlights
␣-Crystallin is an oligomer protein of two subunits, ␣A and ␣B, in a ratio of 3 to 1 for most mammalian lenses
It should be noted that IEF of ␣-crystallin in the native state showed a broad band possibly because of microheterogeneity in the charge or structure
The intermolecular exchange between ␣A- and ␣B-crystallin subunits was demonstrated by IEF in the native state
Summary
␣-Crystallin is an oligomer protein of two subunits, ␣A and ␣B, in a ratio of 3 to 1 for most mammalian lenses. We present evidence of the interoligomeric exchange of the ␣A- and ␣B-crystallins and the stabilization of protein structure by subunit interchange. Intermolecular Exchange of ␣A- and ␣B-Crystallin Subunits higher than 62 °C were made, but under these temperatures aggregation was either too slow or too fast.
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