Continuous dissolution of structure during the unfolding of a small protein.
The unfolding kinetics of many small proteins appears to be first order, when measured by ensemble-averaging probes such as fluorescence and circular dichroism. For one such protein, monellin, it is shown here that hidden behind this deceptive simplicity is a complexity that becomes evident with the use of experimental probes that are able to discriminate between different conformations in an ensemble of structures. In this study, the unfolding of monellin has been probed by measurement of the changes in the distributions of 4 different intramolecular distances, using a multisite, time-resolved fluorescence resonance energy transfer methodology. During the course of unfolding, the protein molecules are seen to undergo slow and continuous, diffusive swelling. The swelling process can be modeled as the slow diffusive swelling of a Rouse-like chain with some additional noncovalent, intramolecular interactions. Here, we show that specific structure is lost during the swelling process gradually, and not in an all-or-none manner, during unfolding.
Jha
Santosh Kumar
SK
National Centre for Biological Sciences, Tata Institute of Fundamental Research, Bangalore 560065, India.
Dhar
Deepak
D
Krishnamoorthy
Guruswamy
G
Udgaonkar
Jayant B
JB
D004058:Diffusion; D031541:Fluorescence Resonance Energy Transfer; D007700:Kinetics; D015335:Molecular Probes / Q000378:metabolism; D050505:Mutant Proteins / Q000378:metabolism; D009579:Nitrobenzoates / Q000378:metabolism; D010940:Plant Proteins / Q000737:chemistry* / Q000378:metabolism*; D017510:Protein Folding; D013438:Sulfhydryl Compounds / Q000378:metabolism; D013997:Time Factors; D014364:Tryptophan / Q000378:metabolism
D015335:Molecular Probes; D050505:Mutant Proteins; D009579:Nitrobenzoates; D010940:Plant Proteins; D013438:Sulfhydryl Compounds; C011136:thionitrobenzoic acid; D014364:Tryptophan