posted on 2017-01-17, 00:00authored byWeiying Zhu, Timothy A. Keiderling
The reformation of secondary structure for unfolded, disulfide reduced hen egg white lysozyme
(HEWL) upon interaction with surfactants was studied using CD, fluorescence and IR (infrared)
techniques. Equilibrium CD studies showed that reduced HEWL when mixed with negatively
charged surfactants, such as SDS (sodium dodecyl sulfate), gradually regains average helical
structure to a level equivalent to that obtained for the oxidized form also in SDS, but both forms
lose tertiary structure in such environments. This non-native structure recovery process begins
with monomer surfactant interaction but at higher concentrations is in part dependent on micelle
formation, with the helical fraction reaching its maximum value with each surfactant only above
the CMC. Fluorescence changes were more complex, evidencing an intermediate state at lower
surfactant concentration. With positively charged surfactants the degree of helicity recovered
was less, and the intermediate state in fluorescence was not seen. Stopped flow dynamics studies
showed the CD kinetics fit to two exponentials as did the fluorescence. The faster steps in CD
and fluorescence detected kinetics appear to be correlated which suggests formation of an
intermediate on rapid interaction of the micelle and protein. The second step then reflected
attainment of a stable surfactant solvated state which attains maximum helicity and moves the
Trps to a more hydrophobic environment, which may occur in independent steps, as the slower
kinetics are not well correlated.
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Publisher Statement
This article may not exactly replicate the final version published in the APA journal. It is not the copy of record. The definitive version is available through Elsevier at DOI:10.1016/j.bbapap.2012.11.010