Pressure-Induced Conformational Changes of β-Lactoglobulin by Variable-Pressure Fourier Transform Infrared Spectroscopy

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Abstract
Pressure-induced conformational changes in D2O solutions of the two genetic variants of β-lactoglobulin A (β-lg A) and β-lactoglobulin B (β-lg B) and an equal mixture of both variants (β-lg A+B) were studied by employing variable-pressure Fourier transform infrared (VP-FTIR) spectroscopy. Changes in the secondary structure of β-lg A were observed at lower pressure compared to β-lg B, indicating that β-lg A had a more flexible structure. During the decompression cycle β-lg A showed protein aggregation, accompanied by an increase in α-helical conformation. The changes in the secondary structure of β-lg B with the pressure were minor and for the most part reversible. Upon decompression no aggregation in β-lg B was observed. Increasing the pressure from 0.01 to 12.0 kbar of a solution containing β-lg A+B resulted in substantial broadening of all major amide I bands. This effect was partially reversed by decreasing the hydrostatic pressure. β-lg A+B underwent less aggregate formation than β-lg A, possibly as a result of protein−protein interactions between β-lg A and β-lg B. Hence, it is likely that the functional or biological attributes of β-lg proteins may be affected in different ways by hydrostatic pressure. Keywords: Fourier transform infrared spectroscopy; β-lactoglobulin; pressure; secondary structure

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