Abstract
α-Lactalbumin (α-La) undergoes considerable structural changes upon loss of bound Ca2+ at acidic pH, leaving α-La in a molten globule structure. Using fluorescence the present work provides more insight into the structural transition of α-La at acidic pH leading to protein aggregation, most likely caused by a combination of hydrophobic and electrostatic interactions. The rate of aggregation is determined by the protein concentration and temperature applied. Availability of Ca2+ stabilises the protein, and thus prevent aggregation at pH values as low as pH 2.9. In contrast, presence of Cu2+ induces a destabilisation of the protein, which can be explained by a binding to the Zn2+ binding site in α-La, possibly resulting in structural alterations of the protein. In general, presence of anions destabilise α-La at pH values below pI, with SO4 2− exhibiting the strongest effect on the protein stability, thus correlating well with the Hofmeister series. At more acidic pH values far from pI, α-La becomes more stable towards ion induced aggregation, since higher ion activity is required to efficiently screen the charges on the protein surface. The results presented in this paper provide detailed knowledge on the external parameters leading to aggregation of α-La at acidic pH, thus permitting rational design of the aggregation process.
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Acknowledgements
Special thanks are regarded to John Sørensen, Hans Bertelsen and Kristian Albertsen from Arla Foods amba for the invaluable collaboration and constructive discussions. Furthermore, Poul Larsen from Aalborg University is acknowledged for his help in obtaining the confocal microscopy results.
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Pedersen, J.B., Fojan, P., Sorensen, J. et al. Towards Control of Aggregational Behaviour of α-Lactalbumin at Acidic pH. J Fluoresc 16, 611–621 (2006). https://doi.org/10.1007/s10895-006-0088-6
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DOI: https://doi.org/10.1007/s10895-006-0088-6