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R. A. Kore, P. Santhoshkumar, K. Sharma, E. C. Abraham; Structural, Functional, and Hydrodynamic Properties of alphaA-Crystallin Mutants Causing Congenital Cataracts. Invest. Ophthalmol. Vis. Sci. 2010;51(13):4617.
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© ARVO (1962-2015); The Authors (2016-present)
Pediatric cataract of the congenital type is the most common cause of childhood blindness. Mutations in 22 different genes have been identified to be associated with congenital cataracts and, among them, 8 mutants belong to αA-crystallin. To explain how each mutation in αA-crystallin leads to the development of cataract, structural, functional, hydrodynamic and interactive properties of the mutants were studied.
αA-crystallin (αA-wt) and its site-directed mutants, namely, R12C, R21L, R21W, R49C, R54C, R116C and R116H were generated by Quick-Change site-directed mutagenesis kit, expressed in E coli BL21 (DE3) PLys S cells, and purified by size-exclusion chromatography. Molar mass, hydrodynamic radius (Rh), and polydispersity index (PDI) were assessed by dynamic light scattering measurements, chaperone activity was measured with ADH and β-crystallin as target proteins. Conformational studies included CD measurements and TNS binding and the interaction of the mutants with αB-crystallin was investigated by the interactive CD approach.
The average molecular mass and mass across the peak for αA-wt and the mutants showed substantial increase in R116C and R116H, moderate increase in R12C, slight increase in R21W and R54C and no increase in R21L and R49C. PDI and Rh values were significantly increased only in R116C and R116H. Relative chaperone activity was deceased in R12C, R116C and R116H, but remained unchanged in all other mutants. Changes in the secondary structure in the form of an increase in the α-helix content were observed in R21W, R21L, R116C and R116H. Tertiary structural changes were evident in R21W, R54C, R116C and R116H. Maximum level of interaction with αB-wt was shown by R116H, R21W, R116C and R21L, in that order; the same mutants showed the highest level of secondary structure change.
Although a specific change in αA-crystallin behavior that is common to all the mutants was not observed, each mutant, however, showed one or more perturbation as probable cause of cataract. The highly conserved residue R116 which exists in the "α-crystallin" domain remains as a "hot spot" showing substantial changes in its oligomeric structure after its mutation to Cys or His. Comparison of R116C and R116H, strongly suggests that mutation of R to C is not essential for showing such drastic changes in the αA-crystallin structure.
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