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J. I. Clark, J. G. Ghosh; The Functional Domains in Human B Crystallin in Development and Maintenance of Lens Transparency. Invest. Ophthalmol. Vis. Sci. 2007;48(13):1523.
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© ARVO (1962-2015); The Authors (2016-present)
To define the spatial organization of the interactive domains in human αB crystallin. The interactive domains are important for chaperone activity against protein aggregation in the Unfolding Protein Response (UPR), for complex assembly, and for stabilization of cytoskeletal proteins during development and maintenance of lens cell transparency.Introduction: αB crystallin consists of 175 amino acids organized in an α-crystallin core domain with N- and C- terminal extensions which are the fundamental features of all sHSP. In lens cells, short range (glass-like) order of cytoplasmic proteins is mediated, in part, by functional interactions between αB crystallin and structural proteins including ß/γ crystallins and cytoskeletal proteins. The interactive sequences in α-crystallins are the basis for the function of sHSP in lens cells.
Protein pin arrays identified the interactive sequences in human αB crystallin. To characterize the spatial organization of the interactive domains, the sequences were mapped to a 3-D homology model constructed using Molecular Operating Environment (MOE) software (Ghosh & Clark (2005) Protein Sci.14:684). Subunit-subunit and subunit-substrate affinities were quantified using Surface Plasmon Resonance (SPR). Mutations in the interactive domains were evaluated for their effects on complex assembly and protection against protein aggregation.
Seven interactive sequences in human αB crystallin were identified using the protein pin arrays. Three interactive sequences map to the N- and C- terminal extensions and four map to the exposed beta strands on the surface of the α-crystallin core domain. A Walker B motif forms an interactive groove between the ß4 and ß8 strands of the core domain and an "IXI" motif is in the C-terminus. Interactive sequences for cytoskeletal and cytoplasmic proteins map to similar domains on the surface of the 3-D homology model. Interactions with cytoskeletal proteins are favored at physiological temperatures and interactions with unfolding cytoplasmic proteins are favored at high temperatures.
The interactive sequences in the core α-crystallin domain of αB crystallin form a surface interface for cytoskeletal elements and for unfolding proteins. The relative strength of the interactions with temperature accounts for the function of αB crystallin in lens cells.
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