Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 6/23/2003
Publication Date: 12/19/2003
Citation: Qi, P.X., Wickham, E.D., Farrell Jr, H.M. 2003. The importance of the c-terminal region of bovine b-casein [abstract]. 17th Symposium of the Protein Society. 12:193.
Technical Abstract: To understand the importance of the C-terminal region on the structure and stability of bovine beta-casein, fragment 1-192 (f1-192) of beta-casein obtained by chymosin digestion was examined and characterized using circular dichroism (CD) under various temperature and solvent conditions. Analytical ultracentrifugation results indicated negligible degree of self-association in f1-192 compared to the whole protein in the temperature range of 2 - 37 degrees C. CONTIN analysis of the CD data revealed little change in the overall secondary structural content in f1-192 relative to whole beta-casein, i.e. 5-10% alpha-helix, 31-35% turns, and 25-29% extended sheet from 5 to 70 degrees C. The temperature dependence of the CD spectra showed two distinctive conformational transitions at 12 and 34-36 degrees C, whereas four transitions were found in the intact protein at 10, 33, 40 and 78 degrees C. The transition at 12 degrees C may represent a general conformational change or cold denaturation in much the same fashion as the 10 degrees C transition in whole beta-casein. The transition at 34-36 degrees C is more likely the reflection of hydrophobic changes in the core of f1-192. Results obtained in this work suggest possible secondary structural disruption of beta-casein upon its C-terminal deletion. Furthermore, it has been demonstrated unambiguously that the C-terminal tail peptide (f193-209) is essential for the self-association and the formation of a complex with 8-anilino-1-naphthalene sulfonic acid (ANS). These results may provide further insights on the critical role of the C-terminal region in the natural cellular function of beta-casein as well as in the whole casein micelle assembly.