To have better understanding of the influence of sugar stereochemistry on protein behavior in an aqueous environment, we examined the effect of three stereoisomeric aldohexoses: D-glucose, D-galactose and D-mannose on the micellization of beta casein (β-Cas)1,2 using pyrene as a fluorescent probe for the formation of hydrophobic domains. Pyrene excitation spectra were recorded for several sets of samples with rising protein concentration (0-5mg/ml), each set with a different co-solute type and concentration (about 0, 0.5, 0.75 and 1 molal for every sugar and 0.5 molal for urea). Critical micellization concentration (CMC) and cooperativity of micellization were evaluated according to changes in Pyrene spectrum as it shifts from the aqueous environment to the hydrophobic cores of β‑Cas micelles. All sugars examined lowered the CMC of β-Cas with increasing sugar concentration and with diminishing degree of effectiveness (Glu > Gal > Man) which correlates well with the sugars’ dynamic hydration number defined by Uedaira3 and correlates negatively with their hydrophobic to hydrophilic molecular surface ratio4. These results support the hypothesis that sugars affect protein self-assembly through both changes in water structure and by hydrophobic interactions, both of which are evidenced to be highly sensitive to sugar stereochemistry.
Principal investigator: Prof. Yoav D. Livney livney@technion.ac.il
References
1. Livney, Y. D.; Schwan, A. L.; Dalgleish, D. G., Journal of Dairy Science 87, (11), 3638-3647. 2004,
2. Portnaya, I.; Cogan, U.; Livney, Y. D.; Ramon, O.; Shimoni, K.; Rosenberg, M.; Danino, D., Journal of Agricultural and Food Chemistry 54, (15), 5555-5561. 2006,
3. Uedaira, H.; Uedaira, H.; Ikura, M., Bulletin of the Chemical Society of Japan 62, (1), 1-4.1989,
4. Miyajima, K.; Machida, K.; Nakagaki, M., 58, 2595-2599. 1985,
