Biophysical Society Thematic Meeting - October 25-30, 2015

Polymers and Self Assembly: From Biology to Nanomaterials Poster Session II

39-POS Board 39 k-Casein from Bovine Milk: From Natural to Pathological Assemblies Silvia Vilasi 1 , Giacoma C. Rappa 1 , Rita Carrotta 1 , Claudio Canale 2 , Pier L. San Biagio 1 , Donatella Bulone 1 . 1 National Research Council, Palermo, Italy, 2 Italian Institute of Technology, Genova, Italy. Casein is the best-characterised milk protein and, in bovine milk, it constitutes over 70–80% of total protein content. In milk, casein exists as large micelle-like complex that comprise four unrelated proteins (αs1-, αs2-, β- and κ-casein) and calcium phosphate. Crucial for the integrity of the protein complex is the k-casein which is responsible for the steric stability of the casein micelles through coating of the structure. All the caseins, αs1-, αs2, β- and κ adopt so extremely open and flexible conformations to be considered full members of the class of intrinsically disordered proteins (IDPs). However, k casein presents special structural features that may reflect in different self-association pathways, each one related to a specific function and biological role. In particular, the presence of the two Cys residues, Cys11 and Cys88, creates a complex disulphide bonding pattern between κ-casein molecules causing heterogeneous polymerization. In native environment, the heterogeneous polymers (from monomers to octamers) further associate through several kinds of interactions in multimeric colloidal systems. On the other hand, it has been demonstrated that κ-casein is able to form amyloid fibrils both in vitro and in vivo, and this is probably the principal cause of corpora amylacea (CA) occurring in calcified stones in mammalian glands. Here, by using several biophysical methods and bioinformatic tools, we investigated how the varying of environmental conditions can determine the different k-casein fate: from natural assembly to pathological amyloid fibrils. Moreover, we demonstrated that the two different self- association regimes are reached in conditions in which specific interactions, hydrogen bond or hydrophobic, became predominant on the others.

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