The role of protein denaturation energetics and molecular chaperones in the aggregation and mistargeting of mutants causing primary hyperoxaluria type I.

[primary hyperoxaluria type 1]

Primary hyperoxaluria type I (PH 1 ) is a conformational disease which result in the loss of alanine :glyoxylate aminotransferase (AGT ) function . The study of AGT has important implications for protein folding and trafficking because PH 1 mutants may cause protein aggregation and mitochondrial mistargeting . We herein describe a multidisciplinary study aimed to understand the molecular basis of protein aggregation and mistargeting in PH 1 by studying twelve AGT variants . Expression studies in cell cultures reveal strong protein folding defects in PH 1 causing mutants leading to enhanced aggregation , and in two cases , mitochondrial mistargeting . Immunoprecipitation studies in a cell-free system reveal that most mutants enhance the interactions with Hsc 70 chaperones along their folding process , while in vitro binding experiments show no changes in the interaction of folded AGT dimers with the peroxisomal receptor Pex 5 p . Thermal denaturation studies by calorimetry support that PH 1 causing mutants often kinetically destabilize the folded apo-protein through significant changes in the denaturation free energy barrier , whereas coenzyme binding overcomes this destabilization . Modeling of the mutations on a 1 .9 Ã… crystal structure suggests that PH 1 causing mutants perturb locally the native structure . Our work support that a misbalance between denaturation energetics and interactions with chaperones underlie aggregation and mistargeting in PH 1 , suggesting that native state stabilizers and protein homeostasis modulators are potential drugs to restore the complex and delicate balance of AGT protein homeostasis in PH 1 .

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primary hyperoxaluria type 1

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