Structure of β-casein micelles

beta-casein is a flexible milk protein which forms micelles. Up to now their structure was controversial. Small-angle neutron scattering was used to determine the protein conformation in the aggregates. Whatever the mean aggregation number, the scattering profiles show that beta-casein micelles are spherical and keep an almost constant radius of 135 Angstrom. They consist of a relatively large and dense core surrounded by a shell of much lower density. In the latter, hydrophilic protein strands and loops protrude in the solvent as polymers grafted on a surface. The core contains most of the hydrophobic residues and some hydrophilic ones. Though its density increases with the aggregation number it is never compact. (C) 1998 Elsevier Science B.V. All rights reserved.