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Monitoring Protein Folding and Unfolding Pathways through Surface Hydrophobicity Changes Using Fluorescence and Circular Dichroism Spectroscopy

J. Lamba1, S. Paul1,2, V. Hasija1, R. Aggarwal1, and T. K. Chaudhuri1*

1Department of Biochemical Engineering and Biotechnology, Indian Institute of Technology Delhi, Hauz Khas, New Delhi 110016, India; E-mail: tapan@dbeb.iitd.ac.in

2Department of Biotechnology and Medical Engineering, National Institute of Technology Rourkela, Rourkela 769008, India

* To whom correspondence should be addressed.

Received August 4, 2008; Revision received November 8, 2008
In the present study we have investigated the characteristics of folding and unfolding pathways of two model proteins, ovalbumin and α-lactalbumin, monitored through the changes in surface hydrophobicity using fluorescence and circular dichroism spectroscopy. In the unfolding process, it was observed that ovalbumin and α-lactalbumin followed a three state transition pathway involving an intermediate state having high surface hydrophobicity. The intermediate state has also been characterized by circular dichroism spectroscopy, and it was found that the intermediate retained almost the same secondary structure as the native proteins, and therefore it can be referred to as molten globule state. The refolding process was monitored using fluorescence and circular dichroism spectroscopy, and it was observed that the refolding of α-lactalbumin was reversible and proceeded through the accumulation of similar type of intermediates as observed during its unfolding pathway. However, on refolding from the guanidine hydrochloride-denatured state, ovalbumin reached a different folded state.
KEY WORDS: surface hydrophobicity, protein unfolding, folding intermediate, fluorescence and circular dichroism spectroscopy, extrinsic fluorescence spectroscopy

DOI: 10.1134/S0006297909040063