Importance of C-Terminal Region of Bovine β-Casein

Abstract

Bovine β-casein (β-CN) with the C-terminal truncated by chymosin digestion, 1-192 fragment (β-CN-(f1-192)), was examined using circular dichroism (CD) under various temperature and solvent conditions. The effect of C-terminal deletion on the structure and stability of the parent protein, β -casein (β-CN), is analyzed and discussed. Analytical ultracentrifugation results showed reduced degree of self -association in β-CΝ-(f1-192) compared to whole β-casein. CONTIN/LL analysis of the CD data revealed clear changes in the overall secondary structural content in β-CΝ-(f1-192) in the temperature range studied (5 to 70°C). Results obtained in this work suggest significant secondary structure disruption of β-casein upon its C-terminal deletion. It has been shown that 80% trifluoroethanol (TFE) at low temperatures (≤ 25°C) can effectively induce α-helical content in β-CΝ-(f1-192), to the same level as that of β-CN. In addition, sodium dodecyl sulfate (SDS) at greater than micellar concentration is capable of refolding β-CΝ-(f1-192). Temperature dependence of these induced structures was also studied. Furthermore, binding experiments with the common hydrophobic probe-8-Anilino-1-naphthalene sulfonate (ANS) illustrated that β-CN -(f1-192) is nearly incapable of binding to ANS. These results clearly demonstrated that the tail peptide, β-CN-(f193-209) is important in maintaining the hydrophobic core of β-CN.U.S. government work.