Implication of C-terminal deletion on the structure and stability of bovine beta-casein.

Bovine beta-casein (beta-CN) with its C-terminal truncated by chymosin digestion, beta-CN-(f1-192), was examined and characterized using circular dichroism (CD) under various temperature conditions. CONTIN/LL analysis of the CD data revealed significant secondary structure disruption in beta-CN-(f1-192) relative to its parent protein,beta-CN, in the temperature range (5 degrees to 70 degrees C) studied. Near-UV CD spectra indicated significant temperature dependent structural changes. Analytical ultracentrifugation results showed significant reduction but not complete abolishment of self-association in beta-CN-(f1-192) compared to whole beta-casein at 2 degrees -37 degrees C. Furthermore, binding experiments with the common hydrophobic probe - 8-anilino-1- naphthalene sulfonic acid (ANS) illustrated that beta-CN-(f1-192) is nearly incapable of binding to ANS relative to whole beta-CN, suggesting a nearly complete open overall tertiary structure brought about by the C-terminal truncation. It has been demonstrated clearly that the tail peptide beta-CN-(f193-209) is important in maintaining the hydrophobic core of beta-CN but the residual association observed argues for a minor role for other sites as well.