Organization and dynamics of BLA in solution and host assemblies
Centre for Cellular and Molecular Biology
Hyderabad 500 007, India
The discovery of intrinsically disordered yet functional proteins has altered the paradigm of structure-function relationship of proteins. In view of this, monitoring the dynamics of proteins, not only in ordered forms but also in disordered forms, such as the molten globule, assumes relevance. Bovine a-lactalbumin (BLA) is a small acidic Ca2+-binding protein (mol. wt. 14,200) present in milk and functions as a specificity modifier of galactosyltransferase . It adopts a milieu of molten globule form under various conditions  and we have studied the molten globule states adopted at acidic pH and in the apo-state [2, 3]. We have utilized wavelength-selective fluorescence approach to monitor the organization and dynamics of BLA under such molten globule forming conditions [2, 3]. Interestingly, BLA forms molten globule under conditions of constrained environment such as when encapsulated in reverse micelles. We have monitored the effect of hydration on the organization and dynamics of encapsulated BLA. BLA specifically interacts with negatively charged membranes and the membrane-bound protein exhibits a molten globule conformation. Tryptophans in BLA exhibit differential red edge excitation shift (REES)  upon binding to negatively charged and zwitterionic membranes, implying differential rates of solvent relaxation around the tryptophan residues. Our results utilizing fluorescence anisotropy and depth analysis by the parallax approach of the tryptophans further support the differential organization and dynamics of the membrane-bound BLA forms. In addition, dipole potential measurements upon BLA binding to membranes and docking studies of BLA with phosphatidylglycerol headgroup provide useful insight into BLA membrane interactions. These results assume significance in the light of antimicrobial and tumoricidal functions of a-lactalbumin [5,6].
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