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Monomerization and Aggregation of β-lactoglobulin Under Adverse Condition: A Fluorescence Correlation Spectroscopic Investigation

Monomerization and Aggregation of β-lactoglobulin Under Adverse Condition: A Fluorescence Correlation Spectroscopic Investigation

Bhaswati Sengupta, Nilimesh Das, Pratik Sen

Biochim Biophys Acta Proteins Proteom. 2018 Feb;1866(2):316-326.

PMID: 29155106

Abstract:

β-Lactoglobulin is one of the major components of bovine milk and it remains in a dimeric form under physiological conditions. The present contribution elucidates the structural change of β-lactoglobulin at pH7.4 under the action of guanidine hydrochloride (GnHCl) and heat at the single molecular level. The only free cysteine (Cys-121) of β-lactoglobulin has been tagged with 7-diethylamino-3-(4-maleimidophenyl)-4-methylcoumarin (CPM) for this purpose. The dimeric structure of β-lactoglobulin found to undergoes a monomerization prior to the unfolding process upon being subjected to GnHCl. The hydrodynamic diameter of the native dimer, native monomer and the unfolded monomer has been estimated as ~55Å, ~29Å and ~37Å, respectively. The free energy change for the monomerization and denaturation are respectively 1.57kcalmol-1 and 8.93kcalmol-1. With change in temperature, development of two types of aggregates (small aggregates and large aggregates) was observed, which is triggered by the formation of the monomeric structure of β-lactoglobulin. The hydrodynamic diameters of the smaller and larger aggregates have been estimated to be ~77Å and ~117Å, respectively. The formation of small aggregates turns out to be reversible whereas that of larger aggregates is irreversible. The free energy associated with these two steps are 0.69kcalmol-1 and 9.09kcalmol-1. Based on the size parameters, the smaller and larger aggregates have been proposed to contain ~twenty and ~sixty monomeric units. It has also been concluded that the monomeric subunits retain their native like secondary structure in these aggregates.

Chemicals Related in the Paper:

Catalog Number	Product Name	Structure	CAS Number	Price
AP50863928	β-Lactoglobulin A from bovine milk		50863-92-8	Price
AP76877333	7-Diethylamino-3-(4-maleimidophenyl)-4-methylcoumarin		76877-33-3	Price

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