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a-Crystallin: molecular chaperone and protein surfactant

Journal Article


Abstract


  • Bovine lens α-crystallin has recently been shown to function as a molecular chaperone by stabilizing proteins against heat denaturation (Horwitz, J. (1992) Proc. Natl. Acad. Sci. USA, 89, 10449-10453). An investigation, using a variety of physico-chemical methods, is presented into the mechanism of stabilization. α-Crystallin exhibits properties of a surfactant. Firstly, a plot of conductivity of α-crystallin versus concentration shows a distinct inflection in its profile, i.e., a critical micelle concentration (cmc), over a concentration range from 0.15 to 0.17 mM. Gel chromatographic and 1H-NMR spectroscopic studies spanning the cmc indicate no change in the aggregated state of α-crystallin implying that a change in conformation of the aggregate occurs at the cmc. Secondly, spectrophotometric studies of the rate of heat-induced aggregation and precipitation of alcohol dehydrogenase (ADH), βL- and γ-crystallin in the presence of α-crystallin and a variety of synthetic surfactants show that stabilization against precipitation results from hydrophobic interactions with α-crystallin and monomeric anionic surfactants. Per mole of subunit or monomer, α-crystallin is the most efficient at stabilization. α-Crystallin, however, does not preserve the activity of ADH after heating. After heat inactivation, gel permeation HPLC indicates that ADH and α-crystallin form a high molecular weight aggregate. Similar results are obtained following incubation of βL- and γ-crystallin with α-crystallin. 1H-NMR spectroscopy of mixtures of α- and βL-crystallin, in their native states, reveals that the C-terminus of βB2-crystallin is involved in interaction with α-crystallin. In the case of γ- and α-crystallin mixtures, a specific interaction occurs between α-crystallin and the C-terminal region of γB-crystallin, an area which is known from the crystal structure to be relatively hydrophobic and to be involved in intermolecular interactions. The short, flexible C-terminal extensions of α-crystallin are not involved in specific interactions with these proteins. It is concluded that α-crystallin interacts with native proteins in a weak manner. Once a protein has become denatured, however, the soluble complex with α-crystallin cannot be readily dissociated. In the aging lens this finding may have relevance to the formation of high molecular weight crystallin aggregates. © 1994.

UOW Authors


  •   Truscott, Roger

Publication Date


  • 1994

Citation


  • Carver, J. A., Aquilina, J. A., Cooper, P. G., Williams, G. A., & Truscott, R. J. W. (1994). a-Crystallin: molecular chaperone and protein surfactant. Biochimica et Biophysica Acta (BBA)/Protein Structure and Molecular, 1204(2), 195-206. doi:10.1016/0167-4838(94)90009-4

Scopus Eid


  • 2-s2.0-0028181093

Web Of Science Accession Number


Start Page


  • 195

End Page


  • 206

Volume


  • 1204

Issue


  • 2

Abstract


  • Bovine lens α-crystallin has recently been shown to function as a molecular chaperone by stabilizing proteins against heat denaturation (Horwitz, J. (1992) Proc. Natl. Acad. Sci. USA, 89, 10449-10453). An investigation, using a variety of physico-chemical methods, is presented into the mechanism of stabilization. α-Crystallin exhibits properties of a surfactant. Firstly, a plot of conductivity of α-crystallin versus concentration shows a distinct inflection in its profile, i.e., a critical micelle concentration (cmc), over a concentration range from 0.15 to 0.17 mM. Gel chromatographic and 1H-NMR spectroscopic studies spanning the cmc indicate no change in the aggregated state of α-crystallin implying that a change in conformation of the aggregate occurs at the cmc. Secondly, spectrophotometric studies of the rate of heat-induced aggregation and precipitation of alcohol dehydrogenase (ADH), βL- and γ-crystallin in the presence of α-crystallin and a variety of synthetic surfactants show that stabilization against precipitation results from hydrophobic interactions with α-crystallin and monomeric anionic surfactants. Per mole of subunit or monomer, α-crystallin is the most efficient at stabilization. α-Crystallin, however, does not preserve the activity of ADH after heating. After heat inactivation, gel permeation HPLC indicates that ADH and α-crystallin form a high molecular weight aggregate. Similar results are obtained following incubation of βL- and γ-crystallin with α-crystallin. 1H-NMR spectroscopy of mixtures of α- and βL-crystallin, in their native states, reveals that the C-terminus of βB2-crystallin is involved in interaction with α-crystallin. In the case of γ- and α-crystallin mixtures, a specific interaction occurs between α-crystallin and the C-terminal region of γB-crystallin, an area which is known from the crystal structure to be relatively hydrophobic and to be involved in intermolecular interactions. The short, flexible C-terminal extensions of α-crystallin are not involved in specific interactions with these proteins. It is concluded that α-crystallin interacts with native proteins in a weak manner. Once a protein has become denatured, however, the soluble complex with α-crystallin cannot be readily dissociated. In the aging lens this finding may have relevance to the formation of high molecular weight crystallin aggregates. © 1994.

UOW Authors


  •   Truscott, Roger

Publication Date


  • 1994

Citation


  • Carver, J. A., Aquilina, J. A., Cooper, P. G., Williams, G. A., & Truscott, R. J. W. (1994). a-Crystallin: molecular chaperone and protein surfactant. Biochimica et Biophysica Acta (BBA)/Protein Structure and Molecular, 1204(2), 195-206. doi:10.1016/0167-4838(94)90009-4

Scopus Eid


  • 2-s2.0-0028181093

Web Of Science Accession Number


Start Page


  • 195

End Page


  • 206

Volume


  • 1204

Issue


  • 2