Casein sequence

Ribadeau-Dumas, B., Brignon, F., Grosclaude, F. and Mercier, J.-C. 1972. Primary structure of bovine, 3-casein. Sequence complete. Eur. J. Biochem. 25, 505-514 (French). 

When homologous ots2-casein sequences were compared, even more insertion/deletion events were required to optimize homology (Stewart et al., 1987). These features contrast with the findings on the (3-... 

Han N, Jarvinen KM, Cocco RR, Busse PJ, Sampson HA, Beyer K (2008). Identification of amino acids critical for IgE-binding to sequential epitopes of bovine K-casein and the similarity of these epitopes to the corresponding human K-casein sequence. Allergy, 63 198-204. 

The progress of proteolysis can be followed by electrophoretic and chromatographic methods, e. g., via the peptide pattern obtained with the help of RP-HPLC (Fig. 10.29) and via changes in concentration of individual peptides which correspond to certain casein sequences (Table 10.33) and can serve as an indicator of the degree of cheese ripening. 

HSFl phosphorylation must be sensitive to nonheat inducers of HSF-DNA binding activity because HSFl phosphorylation can be achieved at 37 °C by other inducers of the HS response. HSF 1 contains polypeptide sequences that could serve as substrates for well characterized protein kinases, but few of these are known to be heat inducible. One family of protein kinases, the S6 protein kinases, have already been shown to exhibit heat inducible activity however, their peak level of activity during HS occurs well after the maximal induction of HSF phosphorylation (Jurivich et al., 1991). Thus, other protein kinases are likely to be directly linked to the phosphorylation of HSF. Some of the putative protein phosphorylation sites on HSF include motifs for protein kinase C, casein kinase, and enterokinase. There are tyrosine sequences that match substrates for known tyrosine kinases, but whether these residues are accessible to phosphorylation is not established. 

These studies suggest that the caseins, synucleins, and tau have natively unfolded structures in which the sequences are based largely on the PPII conformation and are held together in a loose noncooperative fashion. However, rather than describing them as random coil ,... 

All the described properties of such a s-fraction of poly(NVCl-co-NVIAz) synthesized at the temperature above the PST of the reacting system allowed us to draw the conclusion that the chains of this type had the comonomer sequence, which at the temperatures above the conformation transition facilitated the formation of polymer particles, where H-blocks are in the interior shielded by the P-blocks against additional intermolecular association. Such a behaviour of this copolymer in aqueous media is close to that of oligomeric proteins similar to casein [46] possessing a rather hydrophobic core surrounded by the polar segments. 

The most abundant milk protein is casein, of which there are several different kinds, usually designated a-, (1-, and K-casein. The different caseins relate to small differences in their amino acid sequences. Casein micelles in milk have diameters less than 300 nm. Disruption of the casein micelles occurs during the preparation of cheese. Lactic acid increases the acidity of the milk until the micelles crosslink and a curd develops. The liquid portion, known as whey, containing water, lactose and some protein, is removed. Addition of the enzyme rennet (chymosin) speeds up the process by hydrolysing a specific peptide bond in K-casein. This opens up the casein and encourages further cross-linking. 

Only proteins that contain proline bind polyphenols. Asano et al. (1982) demonstrated that the haze-forming activity of a protein is roughly proportional to the mole percentage of proline it contains (see Fig. 2.3). DNA has codes for exactly 20 amino acids. If each of these were equally present in a protein, there would be 5 mol% of each one. In fact, most proteins have much less proline than this. There are a few exceptions. Casein has about 8 mol% proline and the grain prolamins (proline-rich, alcohol-soluble proteins) are even higher. Hordein, the barley prolamin, contains about 20 mol% proline. As a result, it readily forms haze with polyphenols and is the main beer haze-active (HA) protein. Hordein contains even more glutamine (Q) than proline (P), and often these amino acids are adjacent in the protein (see Fig. 2.4). In fact, the sequence P-Q-Q-P occurs... 

Caessens, P.W.J.R., de Jongh, H.H.J., Norde, W., Gruppen, H. (1999). The adsorption-induced secondary structure of p-casein and of distinct parts of its sequence in relation to foam and emulsion properties. Biochimica et Biophysica Acta, 1430, 73-83. 

Figure 4.9 Amino acid sequence of bovine atl -casein, showing the amino acid substitutions or deletions in the principal genetic variants (from Swaisgood, 1992).

Primary structure. The primary structures of the four caseins of bovine milk are shown in Figures 4.9-4.12. The sequences of some non-bovine caseins have been established also. 

The caseins are one of the most evolutionarly divergent families of mammalian proteins. Since their function is nutritional, minor amino acid substitutions or deletions are not critical. Holt and Sawyer (1993), who aligned the published sequences of asl-, / - and K-caseins from various... 

Figure 4.15 Ten residue sequences of bovine caseins with a charge density of 0.5 or greater at pH 6.6 (from Swaisgood, 1992).

Phosphorylation occurs in the Golgi membranes of the mammary cell, catalysed by two serine-specific casein kinases. Only certain serines are phosphorylated the principal recognition site is Ser/Thr.X.Y, where Y is a glutamyl and occasionally an aspartyl residue once a serine residue has been phosphorylated, SerP can serve as a recognition site. X may be any amino acid but a basic or a very bulky residue may reduce the extent of phosphorylation. However, not all serine residues in a suitable sequence are phosphorylated, suggesting that there may be a further topological requirement, e.g. a surface location in the protein conformation. 

At all temperatures, asl-CN B and C are insoluble in calcium-containing solutions and form a coarse precipitate at Ca2+ concentrations greater than about 4 mM. asl-CN A, from which the very hydrophobic sequence, residues 13-26, is deleted, is soluble at [Ca2+] up to 0.4 M in the temperature range 1-33°C. Above 33°C, it precipitates but redissolves on cooling to 28°C. The presence of asl-CN A modifies the behaviour of asl-CN B so that an equimolar mixture of the two is soluble in 0.4 M Ca2+ at 1°C asl-CN B precipitates from the mixture at 18°C and both asl-CN A and B precipitate at 33°C. aBl-CN A does not form normal micelles with K-casein. Since asl-CN A occurs at very low frequency, these abnormalities are of little consequence in dairy processing but may become important if the frequency of asl-CN A increases as a result of breeding practices. 

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