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1 Department of Biochemistry and Molecular Biology, Beijing Normal University, Beijing Key Laboratory, Beijing 100875, P.R. China
2 Department of Biological Science and Biotechnology, Tsinghua University, Beijing 100084, P.R. China
(RECEIVED July 29, 2005; FINAL REVISION September 27, 2005; ACCEPTED October 5, 2005)
Human muscle creatine kinase (CK) is an enzyme that plays an important physiological role in the energy metabolism of humans. It also serves as a typical model for studying refolding of proteins. A study of the refolding and reactivation process of guanidine chloridedenatured human muscle CK is described in the present article. The results show that the refolding process can be divided into fast and slow folding phases and that an aggregation process competes with the proper refolding process at high enzyme concentration and high temperature. An intermediate in the early stage of refolding was captured by specific protein molecules: the molecular chaperonin GroEL and
s-casein. This intermediate was found to be a monomer, which resembles the "molten globule" state in the CK folding pathway. To our knowledge, this is the first monomeric intermediate captured during refolding of CK. We propose that aggregation is caused by interaction between such monomeric intermediates. Binding of GroEL with this intermediate prevents formation of aggregates by decreasing the concentration of free monomeric intermediates, whereas binding of
s-casein with this intermediate induces more aggregation.
Keywords: human muscle creatine kinase; monomeric refolding intermediate; aggregation; GroEL;
s-casein
Abbreviations: ANS, 8-anilino-1-naphthalene sulfonate CK, creatine kinase GuHCl, guanidine hydrochloride
Article and publication are at http://www.proteinscience.org/cgi/doi/10.1110/ps.051738406.
Reprint requests to: Hai-Meng Zhou, Department of Biological Science and Biotechnology, Tsinghua University, Beijing 100084, P.R. China; e-mail: zhm-dbs{at}tsinghua.edu.cn; fax: +86-10-6277-2245; or Sen Li, Department of Biochemistry and Molecular Biology, Beijing Normal University, Beijing Key Laboratory, Beijing 100875, P.R. China; e-mail: lisen{at}bnu.edu.cn; fax: +86-10-5880-7721.
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