Effect of a Single AGE Modification on the Structure and Chaperone Activity of Human αB-Crystallin†

Jaya Bhattacharyya, Ekaterina V. Shipova, Puttur Santhoshkumar, K. Krishna Sharma, Beryl J. Ortwerth
2007 Biochemistry  
During aging, human lens proteins undergo several post-translational modifications, one of which is glycation. This process leads to the formation of advanced glycation end products (AGEs) which accumulate with time possibly leading to the formation of cataract. RB-Crystallin, a predominant protein in the lens, is a member of the small heat shock proteins (sHSPs) which are a ubiquitous class of molecular chaperones that interact with partially denatured proteins to prevent aggregation. This
more » ... erone function is considered to be vital for the maintenance of lens transparency and in the prevention of cataract. In the present study, we introduced an analog of the advanced glycation end product, OP-lysine, at the 90th position of a mutated human RB-crystallin (K90C) by covalent modification of the cysteine residue with N-(2-bromoethyl)-3-oxidopyridinium hydrobromide. The AGE-modified K90C-RB-crystallin is termed as K90C-OP. We compared the structural and functional properties of K90C-OP with the original K90C mutant, with K90C chemically modified back to a lysine analog (K90C-AE), and with wild-type human RB-crystallin. Modified K90C-OP showed decreased intrinsic tryptophan fluorescence and bis-ANS binding without significant alterations in either the secondary, tertiary, or quaternary structure. K90C-OP, however, exhibited a reduced efficiency in the chaperoning ability with alcohol dehydrogenase, insulin, and citrate synthase as substrates compared to the other R-crystallin proteins. Therefore, introduction of a single AGE near the chaperone site of human RB-crystallin can alter the chaperoning ability of the protein with only minor changes in the local environment of the protein. FIGURE 1: Schematic representation of the modification of RB-crystallin-K90C to K90C-AE (aminoethylation) and K90C-OP (3oxidopyridinium ethylation). At the top is shown residue 90 of wild-type RB-crystallin and the amino acid sequence (inset).
doi:10.1021/bi701326b pmid:18027913 fatcat:fhtntvqk25c3pde7dh36luifvy