Structure primaire de la caséine α_sl‐bovine

Abstract

I n previous reports [l-51, we have described some of the features of the primary structure of bovine oL,l-casein. I n the present work, the complete amino acid sequence has been established and the salient features of this phosphoprotein have been discussed.I n the polypeptide chain, the region containing the phosphopeptides Tml (Ti -T2), TmlT2 and TmlTl [1,4,5], had only been shghtly studied as yet. Because of the difficulties encountered in the breakdown of these phosphopeptides, hydrolysis with endopeptidases and exopeptidases were performed on both native and dephosphorylated peptides.It was confirmed that peptide TmlT2 contains three hydroxy-amino acids ( 2 Ser, 1 Thr), but, instead of three [l], two phosphorus atoms were found with purified preparations. Partial acid hydrolysis and dephosphorylation using an orthophosphoric-monoester phosphohydrolase indicate that the two seryl residues in this peptide are 0-phosphorylated. The remaining gap in the sequence of the central part of peptide TmlT2 was bridged by studying two fragments obtained by papain digestion of the dephosphorylated preparation.Instead of four serines, postulated earlier from the results of the amino-acid composition of peptide TmlTl [I], five were shown to be present after detailed analysis of the fragments. Since the five phosphate groups could be readily removed by an orthophosphoric-monoester phosphohydrolase, the five seryl residues could be 0-phosphorylated. The fragments obtained after hydrolysis with thermolysin of both native and dephosphorylated peptide TmlTl were further degraded using classical methods for the determination of the amino acid sequence.I n the light of all the results obtained on this phosphoprotein (a,l-casein B), the total number of amino acid residues has been corrected to 199, instead of 198, as reported previously [l-51, and the molecular weight has been calculated to be 23616. The following amino-acid composition; Asp,, Asn,, Thr,, Ser,, SerP,, Glu,,, Gln,,, Pro,,, Gly9, Ma,, Val,,, Met,, Ile,,, Leu,,, Tyr,,, Phe,, LysI4, His,, Trp,, Arg,, indicates that there is a higher number of acidic than basic residues in this protein. On the basis of the intrinsic dissociation constants of titratable groups in proteins [6], the negative net charge of the molecule was estimated to be 22 at pH 6.5 and 28 at pH 8.6. Since Bigelow's parameter for the average hydrophobicity [7] of this protein is 1170, it could be considered to be a hydrophobic protein. The high amount (8.50/,) and uniform distribution of prolyl residues indicate that this protein has limited structuralcoiling possibilities.The polypeptide chain contains three hydrophobic regions, viz. 1-44,90-113 and 132-199. The fist two are characterized by the fact that basic residues predominate over acidic residues. The third region, where most of the aromatic residues are located, contains very few basic residues and is therefore of more acidic character.Two regions, 45-89 and 114-131, are hydrophilic. The former contains more than half of the total acidic residue...

Structure primaire de la caséine β bovine

“…Nous discuterons donc ici les caracteristiques de la mol6-cule qui peuvent &re deduites de la sequence complete representee dans la Fig.4, et nous comparerons cette molecule Q la caseine cxsl dont la structure a 6th determinee Bgalement dans ce laboratoire [6]. Nous rassemblerons, pour terminer cette discussion, les enseignements d'ordre methodologique que nous avons pu tirer de ce travail.…”

Conformation and Some Properties of Bovine αs2-Group-casein

“…aS2-Group-casein was isolated from whole bovine casein by electrostatic affinity chromatography on a column of Amberlite CG-50 according to Snoeren et al S) The proportion of a s2-, ass-and as4-casein in this preparation was estimated to be 3: 4: 3 by slab electrophoresis. !lsl-Casein was preparated by the urea fractionation method of Fox 15 ) and 117.4 for us2-casein from the data of Brignon et al 8 ) Slab electrophoresis. Slab electrophoresis was performed in 5 % acrylamide gel in pH 8.…”

Specific Casein Phosphorylation by a Casein Kinase from Lactating Bovine Mammary Gland

“…From the known sequence of ix,l-casein [15] and by taking into account the specificity of action of the staphylococcal proteinase, which may be expected to have attacked only peptide linkages located on the carboxyl side of glutamyl residues [16], it was possible Table 4. Incorporation of phosphate by casein kinase into peptides produced by treatment of aSl-casein with cyanogen bromide The incorporation of 32P was measured under the conditions described in the text for assay of casein kinase using the butanolextracted fraction I11 enzyme preparation.…”