The association of bovine beta-casein. The importance of the C-terminal region.
Bovine beta-casein exists in the monomer form in solution (pH 6.5, 0.1 M NaCl, 0.5% w/v) at low temperatures, but associates to form polymers at higher temperatures. Gel filtration chromatography at 36 degrees showed that the polymer is large with a hydrodynamic size greater than that of a globular protein with a mol wt of 1.34 times 10(6). Removal of two C-terminal amino acids per molecule decreased the proportion of polymer in the solution, although the chromatographic behavior of the modified beta-casein monomers and polymers was retained. Removal of a 20 amino acid peptide from the C terminus of the beta-casein completely destroyed its ability to form polymers and removed the 8-anilino-1-naphthalenesulfonate binding site. However, deletion of segments of the protein from the N terminus did not decrease the ability of the modified beta-casein to associate, nor did it affect the 8-anilino-1-naphthalenesulfonate binding site greatly. It seems likely that all, or some, of the 20 amino acids at the C terminus are responsible for the associative behavior of beta-casein, possibly by the direct participation of their side chains in hydrophobic bond formation. However, removal of the C-terminal peptides may have disrupted the spatial structure of the native protein so that it could no longer associate normally.
D000595:Amino Acid Sequence; D000817:Anilino Naphthalenesulfonates; D000818:Animals; D001665:Binding Sites; D002364:Caseins; D002417:Cattle; D002850:Chromatography, Gel; D004589:Electrophoresis, Disc; D005260:Female; D007700:Kinetics; D046911:Macromolecular Substances; D010446:Peptide Fragments / Q000032:analysis; D011485:Protein Binding; D013050:Spectrometry, Fluorescence; D013696:Temperature
D000817:Anilino Naphthalenesulfonates; D002364:Caseins; D046911:Macromolecular Substances; D010446:Peptide Fragments