Mutation R120G in alphaB-crystallin, which is linked to a desmin-related myopathy, results in an irregular structure and defective chaperone-like function.
alphaB-crystallin, a member of the small heat shock protein family, possesses chaperone-like function. Recently, it has been shown that a missense mutation in alphaB-crystallin, R120G, is genetically linked to a desmin-related myopathy as well as to cataracts [Vicart, P., Caron, A., Guicheney, P., Li, A., Prevost, M.-C., Faure, A., Chateau, D., Chapon, F., Tome, F., Dupret, J.-M., et al. (1998) Nat. Genet. 20, 92-95]. By using alpha-lactalbumin, alcohol dehydrogenase, and insulin as target proteins, in vitro assays indicated that R120G alphaB-crystallin had reduced or completely lost chaperone-like function. The addition of R120G alphaB-crystallin to unfolding alpha-lactalbumin enhanced the kinetics and extent of its aggregation. R120G alphaB-crystallin became entangled with unfolding alpha-lactalbumin and was a major portion of the resulting insoluble pellet. Similarly, incubation of R120G alphaB-crystallin with alcohol dehydrogenase and insulin also resulted in the presence of R120G alphaB-crystallin in the insoluble pellets. Far and near UV CD indicate that R120G alphaB-crystallin has decreased beta-sheet secondary structure and an altered aromatic residue environment compared with wild-type alphaB-crystallin. The apparent molecular mass of R120G alphaB-crystallin, as determined by gel filtration chromatography, is 1.4 MDa, which is more than twice the molecular mass of wild-type alphaB-crystallin (650 kDa). Images obtained from cryoelectron microscopy indicate that R120G alphaB-crystallin possesses an irregular quaternary structure with an absence of a clear central cavity. The results of this study show, through biochemical analysis, that an altered structure and defective chaperone-like function of alphaB-crystallin are associated with a point mutation that leads to a desmin-related myopathy and cataracts.
Bova
M P
MP
Jules Stein Eye Institute, University of California Los Angeles School of Medicine, Los Angeles, CA 90095-7008, USA.
Yaron
O
O
Huang
Q
Q
Ding
L
L
Haley
D A
DA
Stewart
P L
PL
Horwitz
J
J
D000426:Alcohol Dehydrogenase / Q000378:metabolism; D019943:Amino Acid Substitution; D002942:Circular Dichroism; D020285:Cryoelectron Microscopy; D003459:Crystallins / Q000737:chemistry* / Q000235:genetics* / Q000378:metabolism / Q000648:ultrastructure; D003893:Desmin / Q000235:genetics*; D006801:Humans; D046911:Macromolecular Substances; D018832:Molecular Chaperones / Q000737:chemistry / Q000378:metabolism / Q000648:ultrastructure; D009135:Muscular Diseases / Q000235:genetics*; D020125:Mutation, Missense; D011487:Protein Conformation; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism / Q000648:ultrastructure
D003459:Crystallins; D003893:Desmin; D046911:Macromolecular Substances; D018832:Molecular Chaperones; D011994:Recombinant Proteins; D000426:Alcohol Dehydrogenase