Submitted to: Meeting Abstract
Publication Type: Proceedings
Publication Acceptance Date: July 18, 2006
Publication Date: N/A
Technical Abstract: The caseins of milk form micelles to carry the otherwise insoluble calcium and phosphate which are indispensable nutrients for humans. To better understand the molecular structure and function of casein micelles, we focused on its major component: beta-casein. The assumption that beta-casein is either a random coil or a "rheomorphic" protein, which describes caseins as structurally flexible and formed upon flow, remains controversial. In this work, we report on the association reaction of beta-casein to address the question of whether or not a conformational change in the monomer precedes aggregation, or occurs as a result of aggregation. Circular dichroism (CD), fluorescence and Fourier transformation infrared (FTIR) spectroscopies were used to investigate the temperature-induced changes in the secondary structure of the beta-casein under physiological relevant conditions (water, pH and low ionic strength). The degree of self-association under these conditions was assessed by analytical ultracentrifugation. CD and FTIR results show that the beta-casein may fold considerably prior to self-association, but may further respond to close packing in the polymer. The binding of beta-casein to hydrophobic probe 1-anilino-8-naphthalenesulfonate (ANS) in the fluorescence experiments indicates it may be a "pre-molten globule" protein. Molecular modeling and dynamics simulation techniques were used to not only generate a three-dimensional structure of beta-casein based on these physical chemical data but also to provide insight on the self-association process as well as its function in the formation and stabilization of casein micelles.