Electrostatic Interactions Play a Critical Role in Mycobacterium tuberculosis Hsp16.3 Binding of Substrate Proteins

Q. Mao, D. Ke, and Z. Chang^*

Department of Biological Science and Biotechnology and State Key Laboratory of Biomembranes and Membrane Biotechnology, Tsinghua University, Beijing 100084, P. R. China; fax: 86-10-62785505; E-mail: changzy@mail.tsinghua.edu.cn

^* To whom correspondence should be addressed.

Received January 13, 2001

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Mycobacterium tuberculosis Hsp16.3, a member of a small heat shock protein family, has chaperone-like activity in vitro and suppresses thermally or chemically induced aggregation of proteins. The nature of the interactions between Hsp16.3 and the denatured substrate proteins was investigated. A dramatic enhancement of chaperone-like activity of Hsp16.3 upon increasing temperature was accompanied by decreased ANS-detectable surface hydrophobicity. Hsp16.3 exhibited significantly enhanced chaperone-like activity after preincubation at 100°C with almost unchanged surface hydrophobicity. The interaction between Hsp16.3 and dithiothreitol-treated insulin B chains was markedly weakened in the presence of NaCl but greatly enhanced by the addition of a low-polarity alcohol, accompanied by significantly increased and decreased surface hydrophobicity, respectively. A working model for Hsp16.3 binding to its substrate proteins is proposed.

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KEY WORDS: small heat shock protein, heat pretreatment, chaperone-like activity, surface hydrophobicity

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