Inability of chaperones to fold mutant z

[摘要] Purpose: z-crystallin is a quinone oxido-reductase, recruited inthe eye lens of hystricomorphic rodents and camels. A deletion mutationconstituting the NADPH-binding domain causes congenital cataract in astrain of guinea pigs. The presence of large quantities ofa-crystallin, a molecular chaperone, does not provide any protectionagainst this. In order to investigate whether the underlying reason forthe lack of protection is the formation of a folding-incompetentprotein, we have expressed the mutant protein in a heterologous systemalong with other known chaperones.Methods: We expressed the mutant z-crystallin in E. colialong with other chaperones such as GroEL/ES and DnaK/DnaJ/GrpE and thenanalyzed whether these chaperones could increase the amount of proteinpartitioning into the soluble fraction of E. coli cells.Results: These chaperones were unable to rescue the mutant proteinfrom partitioning into inclusion bodies, although they could increasethe yield of soluble wild-type z-crystallin.Conclusions: The deletion of 34 amino acids, constituting theNADPH-binding domain of z-crystallin, makes the protein incompetentto fold correctly and thus form insoluble aggregates. It perhapssuggests why the mutant strain of guinea pigs have cataract at birtheven though their lenses contain high amounts of a-crystallin. Thisstudy also shows that certain mutations can render proteins incompetentto fold into soluble molecules despite abundant assistance.

[学科分类] 生物化学/生物物理