A-sl-Casein

Alaimo, M.H., Farrell, H.M. Jr., and Germann, M.W. 1999. Conformational analysis of the hydrophobic peptide a-sl-casein (136-196). Bio-chim. Biophys. Acta 1431 410-420. 

D.J. McCormick, M.W. Holmes, D.C. Muddiman, B.J. Madden, Mapping sites of protein phosphorylation by MS utilizing a chemical-enzymatic approach characterization of products from a-Sl casein phosphopeptides, J. Proteome Res., 4 (2005) 424. 

Chatchatee, P., Jarvinen, K.M., Bardina, L., Beyer, K., and Sampson, H.A. 2001a. Identification of IgE- and IgG-binding epitopes on alpha(sl)-casein Differences in patients with persistent and transient cow s milk allergy. J Allergy Clin Immunol 107(2) 379—383. 

Cocco, R.R., Jarvinen, K.M., Sampson, H.A., and Beyer, K. 2003. Mutational analysis of major, sequential IgE-binding epitopes in alpha sl-casein, a major cow s milk allergen. J Allergy Clin Immunol 112(2) 433—437. 

Bovine casein is listed by the International Union of Immunological Societies as a single allergen, Bos d 8. However, it contains four main protein components, a-sl-, a-s2-, 3-, and K-Casein, in approximate proportions of 40% 10% 40% 10%, respectively (Bernard et al. 1998). The fractions obtained after acid coagulation of individual caseins are cross-linked to aggregates called nanoclusters, which combine into micelles. Their central part is hydrophobic and peripheral hydrophilic parts contain sites of phosphorylation. 

The casein family of protein consists of several types of caseins [a-sl, a-s2, and/3-6]. Each of them has its own amino acid composition, genetic variations, and functional properties. The caseins are suspended in milk in a complex called a micelle. 

Casein is the major component (80 per cent) of milk, with molecular weights between 1 and 20kDa and includes four distinct types a-sl, a-s2, (3, and k. Casein is the predominant phosphoprotein that precipitates at pH 4.6 (20°C) and is characterized by an open, random coil structure. By treating acid-precipitated caseins with alkali solution caseinates are produced. Both caseins and caseinates form transparent films from aqueous solutions without any treatment because of their random coil nature and numerous hydrogen bonds. Caseins have shown to be useful in adhesives, micro encapsulation, food ingredients, and pharmaceuticals [31]. 

Kampa, M., Loukas, S., Hatzoglou, A., Martin, P., Martin, P. M., and Castanas, E. (1996). Identification of a novel opioid peptide (Tyr-Val-Pro-Phe-Pro) derived from human alpha SI casein (alpha Sl-casomorphin, and alpha Sl-casomorphin amide). Biochem. J. 319(Pt. 3), 903-908. 

No cysteine residues are found for alpha(sl) and P-caseins do. If any S-S bonds occur within the micelle, they are not the driving force for stabilization. Caseins are among the most hydrophobic proteins, and there is some evidence to suggest that they play a role in the stability of the micelle. It must be remembered that hydrophobic interactions are very temperature sensitive. 

Vreeman, W. J., Visser, S., Slangen, C. J., and van Reel, J. A. M. (1986). Characterization of bovine k—casein fractions and the kinetics of chymosin—induced macropeptide release from carbohydrate—free and carbohydrate—containing fractions determined by high performance gel premeation chromatography. Biochem. J. 240, Sl-91. 

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