Inhibition of amyloid fibrillogenesis and toxicity by a peptide chaperone

Aggregation of proteins in tissues is associated with several diseases, including Alzheimer's disease. It is characterized by the accumulation of amyloid beta peptide (Abeta) in the extracellular spaces of the brain cells, resulting in neuronal death and other pathological changes. alpha-Crystallin, a small heat-shock protein in lens, and a peptide chaperone having the functional site sequence DFVIFLDVKHFSPEDLTVK of alphaA-crystallin may inhibit Abeta fibrillogenesis and toxicity. The peptide chaperone (mini-alphaA-crystallin), having an Abeta interacting domain and a complex solubilizing domain, was shown in previous studies to prevent aggregation of several proteins under denaturing conditions. In this in vitro study, using transmission electron microscopy and thioflavin T binding assay, we show that mini-alphaA-crystallin arrests the fibril formation of Abeta peptides. Mini-alphaA-crystallin also suppresses the toxic action of Abeta on rat pheochromocytoma (PC 12) cells. The wide chaperoning capability of the peptide and its ability to inhibit amyloid fibril formation and suppress toxicity suggest that mini-alphaA-crystallin may serve as a universal chaperone in controlling diseases of protein aggregation, including Alzheimer's disease.

Isolation, expression, and characterization of fully functional nontoxic BiP/GRP78 mutants

Mammalian BiP/GRP78 and Escherichia coli DnaK belong to the highly conserved hsp70 family and function as molecular chaperones in the endoplasmic reticulum or the cytosol, respectively. Induction of murine BiP/GRP78 expression in E. coli leads to growth arrest and cell death, independent of the bacterial strain and vector used. Analysis of various BiP constructs and mutants shows that the dominant-lethal phenotype is induced specifically by the expression of the 13.7-kDa C-terminal domain and abolished by a single substitution in that region. Deletion of that region also results in nontoxic gene products that can be overexpressed and purified to homogeneity. The nontoxic mutants are highly expressed in E. coli, representing up to 20% of the soluble fraction. They are catalytically active, depolymerize upon binding ATP or synthetic peptide, and interact with the J-domain of the DnaJ-like accessory protein, MTJ1, with near wild-type affinity. Our data indicate that the cytotoxic effect encountered during overexpression of recombinant proteins can be caused by a single domain and can be alleviated by a specific mutation or deletion in that region without altering the catalytic properties of the enzyme.

[Experimental study of the influence of disturbing factors and chaperone-like drugs on cataractogenesis]

A comparative experimental study of biomicroscopic appearance of lenses in cataracts of different genesis (age-related, ultraviolet and other radiation-induced or combined) has been performed on animals (mice). It is shown that identical lens opacification can be provoked by aging (endogenous factor), as well as ultraviolet and other radiation exposure (exogenous physical factors). The only differential sign is the severity of the damage. These factors can be arranged in the following ascending order by their damaging ability: aging --> ultraviolet --> gamma rays --> gamma rays + ultraviolet. Anti-cataract effect of a chaperone-like combined drug (N-acetylcarnosin and D-pantetin) has been studied in vivo on a "prolonged" model of induced cataract in rats. The use of the combined drug (1:1 mixture of the two peptides) in the form of ocular instillations and intraperitoneal injections helped slowing the progression of the ultraviolet-induced cataract in vivo.