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A near-native state on the slow refolding pathway of hen lysozyme

Published online by Cambridge University Press:  01 January 1999

SUNITA K. KULKARNI
Affiliation:
School of Biochemistry and Molecular Biology, University of Leeds, Leeds LS29JT, United Kingdom
ALISON E. ASHCROFT
Affiliation:
School of Biochemistry and Molecular Biology, University of Leeds, Leeds LS29JT, United Kingdom
MICHAEL CAREY
Affiliation:
Applied Photophysics Ltd., 203–205 Kingston Road, Leatherhead, Surrey KT227PB, United Kingdom
DIMITRIS MASSELOS
Affiliation:
Oxford Centre for Molecular Sciences, New Chemistry Laboratory, South Parks Road, Oxford OX13QT, United Kingdom
CAROL V. ROBINSON
Affiliation:
Oxford Centre for Molecular Sciences, New Chemistry Laboratory, South Parks Road, Oxford OX13QT, United Kingdom
SHEENA E. RADFORD
Affiliation:
School of Biochemistry and Molecular Biology, University of Leeds, Leeds LS29JT, United Kingdom
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Abstract

The refolding of four disulfide lysozyme (at pH 5.2, 20 °C) involves parallel pathways, which have been proposed to merge at a near-native state. This species contains stable structure in the α- and β-domains but lacks a functional active site. Although previous experiments have demonstrated that the near-native state is populated on the fast refolding pathway, its relevance to slow refolding molecules could not be directly determined from previous experiments. In this paper, we describe experiments that investigate the effect of added salts on the refolding pathway of lysozyme at pH 5.2, 20 °C. We show, using stopped flow tryptophan fluorescence, inhibitor binding, and circular dichroism (CD), that the rate of formation of native lysozyme on the slow refolding track is significantly reduced in solutions of high ionic strength in a manner dependent on the position of the anion in the Hofmeister series. By contrast, the rate of evolution of hydrogen exchange (HX) protection monitored by electrospray ionization mass spectrometry (ESI MS) is unchanged under the refolding conditions studied. The data show, therefore, that at high ionic strengths β-domain stabilization and native state formation on the slow refolding pathway become kinetically decoupled such that the near-native state becomes significantly populated. Thus, by changing the energy landscape with the addition of salts new insights into the relevance of intermediate states in lysozyme refolding are revealed.

Type
Research Article
Copyright
© 1999 The Protein Society

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