Structural differences between bovine A(1) and A(2) β-casein alter micelle self-assembly and influence molecular...

Area of Science:

• Biochemistry
• Food Science
• Protein Chemistry

Background:

• Milk protein genetic variants influence milk functionality.
• Bovine beta-casein (β-CN) A(1) and A(2) variants affect milk gelation.
• These variants differ by a single amino acid substitution at position 67.

Purpose of the Study:

• To investigate the micelle assembly of A(1) and A(2) β-CN variants.
• To assess the protein functionality and molecular chaperone activity of these variants.
• To understand how single amino acid differences impact β-CN properties and milk functionality.

Main Methods:

• Dynamic light scattering and small-angle X-ray scattering for micelle assembly analysis.
• Fluorescence techniques and molecular chaperone assays for protein functionality assessment.
• Comparative analysis of A(1) and A(2) β-CN structures and behaviors.

Main Results:

• A(2) β-CN formed smaller micelles compared to A(1) β-CN.
• The monomer-micelle equilibrium for A(2) β-CN favored the monomer state.
• A(2) β-CN exhibited enhanced molecular chaperone activity, likely due to structural differences (increased polyproline-II helix).

Conclusions:

• A single amino acid substitution significantly alters intrinsically unstructured protein properties like β-CN.
• Differences in micelle assembly and chaperone activity between A(1) and A(2) β-CN explain variations in milk functionality.
• This highlights the impact of genetic variants on milk composition and performance.