Defense Mechanism of cells from stresses

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1-1. We found taht heated HSP90 binds and protects denatured firefly luciferase from irreversible aggregation. Luciferase can be released from the complexes when post-incubated in HSP70, HSP40 and another chaperone contained in reticulocyte lysate.1-2. We found taht monoclonal antibodies specific to the N-terminus of HSP90 bound to both ends of HSP90 dimers. This indicates that HSP90 monomers align side-by-side in an antiparallel fashion and form dimers through their C-termini.1-3. In the budding yeast, the expression level of Hsc82 was found to be reversibly proportional to the degree of stress tolerance.2-1. We have determined tertiary structure of destrin, a cofilin-related protein, by NMR.The structure is similar to that of a unitary segment of gelsolin. The structure provides molecula basis for Ca^<2+> -independent binding of cofilin to actin.2-2. Overexpression of cofilin in Dictyostelium cells induced a number of actin bundles. This was suggested to be a result of transformation from actin meshwork to bundles by cofilin-induced severing of F-actin. We further demonstrated that the bundles contracted in response to osmotic stress.2-3. We found that cofilin was inactivated by phosphorylation of the Ser-32-4. A multicopy suppressor to a cofilin-ts mutant in Saccharomyces cerevisiae was isolated. The suppressor gene SCF1 encodes a WD40-repeat protein which is identidal to Aip1 previously described as an actin-intereating protein. SCF1 is not essential for cell viability.2-5. Biochemical evidence has been obtained that Dictyostelium Aip1 binds to F-actin and seisitizes it to destruction by cofiin.