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Updated: Sep 21, 2026

From Constructs to Crystals – Towards Structure Determination of β-barrel Outer Membrane Proteins
Published on: July 4, 2016
Formation of betaA3/betaB2-crystallin mixed complexes: involvement of N- and C-terminal extensions
P J Werten1, R A Lindner, J A Carver
1Department of Biochemistry, University of Nijmegen, P.O. Box 9101, 6500 HB, Nijmegen, Netherlands.
Abstract:
The sequence extensions of the beta-crystallin subunits have been suggested to play an important role in the oligomerization of these eye lens proteins. This, in turn, may contribute to maintaining lens transparency and proper light refraction. In homo-dimers of the betaA3- and betaB2-crystallin subunits, these extensions have been shown by (1)H-NMR spectroscopy to be solvent-exposed and highly flexible. In this study, we show that betaA3- and betaB2-crystallins spontaneously form mixed betaA3/betaB2-crystallin complexes, which, from analytical ultracentrifugation experiments, are dimeric at low concentrations (<1 mg ml(-1)) and tetrameric at higher protein concentrations. (1)H-NMR spectroscopy reveals that in the betaA3/betaB2-crystallin tetramer, the N-terminal extensions of betaA3-crystallin remain water-exposed and flexible, whereas both N- and C-terminal extensions of betaB2-crystallin lose their flexibility. We conclude that both extensions of betaB2-crystallin are involved in protein-protein interactions in the betaA3/betaB2-crystallin hetero-tetramer. The extensions may stabilize and perhaps promote the formation of this mixed complex.
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