THE BALANCE BETWEEN Hsp70 AND ITS COCHAPERONES Hdj1 AND Bag1 DETERMINES ITS
SUBSTRATE-BINDING ACTIVITY
S. S. Novoselov, T. V. Novosclova, M. V. Verbova, B. A. Margulis, L V. Guzhova
Institute of Cytology RAS, St. Petersburg, Russia;
e-mail: novoselov@mail.cytspb.rssi.ru
Heat shock protein Hsp70 presents one of the most effective cell protective systems. Its protective activity is
mostly due to the fact that Hsp70 is able to restore native conformation of newly synthesized or damaged proteins. Two other proteins.
Hdj1 and Bag1, are involved in the process, allowing Hsp70 to perform binding-release cyclec of target proteins. The aim of this study
was to investigate interactions between cochaperones Hdj1 and Bag1, and the major cell chaperone Hsp in vitro. The accumulation of
Hsp70 and Hdj1 in human erythroleukemia K562 cells was stimulated by heat stress (43°C, 60 min). Cells were collected at certain time
periods after heat stress, and amounts of cell chaperones were measured using Western blotting and ELISA assay. The level of Hsp70
chaperone activity in cell extracts was estimated using original technique. The effects of exogenous cochaperones and of their parts
on this activity were also investigated. The results of the study indicate that Hsp70 chaperone activity is regulated by the level
of its cochaperones, especially Hdj1. At the same time the amount of ATP appears to be critical for functional activity of Hsp70.
Hdj1 and Bag1 peptides, which bind to Hsp70 with high affinity, are able to significally reduce its chaperone activity. This
finding confirms the possibility of using peptide approach for regulation of Hsp70 function at the cellular and organismal levels.
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