Exploring tryptophan dynamics in acid-induced molten globule state of bovine α -lactalbumin: a wavelength-selective fluorescence approach

Kelkar, Devaki A. ; Chaudhuri, Arunima ; Haldar, Sourav ; Chattopadhyay, Amitabha (2009) Exploring tryptophan dynamics in acid-induced molten globule state of bovine α -lactalbumin: a wavelength-selective fluorescence approach European Biophysics Journal, 39 (10). pp. 1453-1463. ISSN 0175-7571

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Official URL: http://www.springerlink.com/content/gxw5755v2041h5...

Related URL: http://dx.doi.org/10.1007/s00249-010-0603-1

Abstract

The relevance of partially ordered states of proteins (such as the molten globule state) in cellular processes is beginning to be understood. Bovine α -lactalbumin (BLA) assumes the molten globule state at acidic pH. We monitored the organization and dynamics of the functionally important tryptophan residues of BLA in native and molten globule states utilizing the wavelength-selective fluorescence approach and fluorescence quenching. Quenching of BLA tryptophan fluorescence using quenchers of varying polarity (acrylamide and trichloroethanol) reveals varying degrees of accessibility of tryptophan residues, characteristic of native and molten globule states. We observed red edge excitation shift (REES) of 6 nm for the tryptophans in native BLA. Interestingly, we show here that BLA tryptophans exhibit REES (3 nm) in the molten globule state. These results constitute one of the early reports of REES in the molten globule state of proteins. Taken together, our results indicate that tryptophan residues in BLA in native as well as molten globule states experience motionally restricted environment and that the regions surrounding at least some of the BLA tryptophans offer considerable restriction to the reorientational motion of the water dipoles around the excited-state tryptophans. These results are supported by wavelength-dependent changes in fluorescence anisotropy and lifetime for BLA tryptophans. These results could provide vital insight into the role of tryptophans in the function of BLA in its molten globule state in particular, and other partially ordered proteins in general.

Item Type:Article
Source:Copyright of this article belongs to Springer-Verlag.
Keywords:Molten Globule; α-lactalbumin; Red Edge Excitation Shift; Fluorescence Quenching; Fluorescence Anisotropy; Fluorescence Lifetime
ID Code:6984
Deposited On:26 Oct 2010 04:50
Last Modified:29 Jan 2011 04:54

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