Chain conformation amino acid amphiphiles

The major casein monomer subunits have random coil conformation that facilitates strong protein-protein interaction via hydrophobic and ionic bonding. The unique amphiphilic structure, which arises from separately clustered hydrophobic and negatively charged (acidic and ester phosphate) amino acid residues along the polypeptide chain, makes them susceptible to pH and Ca ion concentration effects. This amphiphilic nature is probably responsible for the excellent surfactant properties of commercial caseinate in a variety of food applications. 

By inserting appropriate amino acid side chains (e.g., hydrophilic and hydrophobic), it is feasible to construct amphiphilic helices (with two faces that possess different properties). The conformational strategy should take into account the parameters typical of each of the two helices, in particular that 1) The a-helix (Fig. la) is characterized by a fractional number of amino acids per turn (=3.5) and consequently its smallest repeat (i.e., the shortest main-chain length that brings two side chains exactly one on top of the other) is a heptad (7 residues) and 2) in the 3io-helix (Fig. lb), which has an integer number of amino acids per turn (=3.0), a triplet of residues selected carefully will produce the expected amphiphiUcity. 

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