Copresence of Deleted Protein Species Generates Structural Heterogeneity of Ovine alpha(s1)-Casein

Mediterranean river buffalo CSN1S1 gene: search for polymorphisms and association studies

The aim of the present study was to investigate the variability at CSN1S1 locus of the Italian Mediterranean river buffalo and to study possible allele effects on milk yield and its composition. Effects of parity, calving season and month of production were also evaluated. Three single-nucleotide polymorphisms were detected. The first mutation, located at position 89 of the 17th exon (c.628C>T), is responsible for the amino acid change p.Ser178 (B allele)/Leu178 (A allele). The other two polymorphisms, detected at the positions 144 (c.882G>A) and 239 (c.977A>G) of 19th exon, respectively, are silent (3ʹ UTR, untranslated region). Associations between the CSN1S1 genotypes and milk production traits were investigated using 4122 test day records of 503 lactations from 175 buffalo cows. Milk yield, fat and protein percentages were analysed using a mixed linear model. A significant association between the c.628C>T SNP and the protein percentage was found. In particular, the CC genotype showed an average value ~0.04% higher than the CT and TT genotypes. The allele substitution effect of cytosine into thymine was –0.014, with a quite low (0.3%) protein percentage contribution to total phenotypic variance. A large dominance effect was detected. Characterisation of the CSN1S1 transcripts and a method based on MboI amplification created restriction site PCR for a rapid genotyping of c.628C>T are provided.

The occurrence of genetic polymorphism and related non-allelic proteins increases the compositional complexity of goat α((s1)) -CN

A genetic survey on three autochthonous goat breeds reared in Italy was carried out by a proteomic approach. This methodology, further to providing the phenotypic frequency of identified α(s1) genetic variants, allowed to determine (i) the additional constitutive presence of a non-allelic 'α(s1) -casein (CN) F like' protein in goat 'strong' α(s1) variants; (ii) an α(s1) -CN B(2) like protein, expressed at very low quantitative level, in goat 'weak' α(s1) -CN variants, and, as main focus; (iii) the occurrence of a new α(s1) -CN D(1) variant characterised by the lack of α(s1) (f59-69) sequence otherwise encoded by exon 9 in goat α(s1) B(2) reference. The same exon skipping event had been identified since 1990, as responsible of the 'weak quantitative class' of α(s1) -CN D variant (0.6 g/L), while the new α(s1) -CN D(1,) has been 'quantitatively' classified as an 'intermediate' variant, since 1.8 g/L per allele was assessed in the milk.

Comparative analysis of gene sequence of goat CSN1S1 F and N alleles and characterization of CSN1S1 transcript variants in mammary gland

In this paper, we report the full characterization, at DNA and RNA level, of the defective goat CSN1S1 F and N alleles and an extensive comparison with the A allele counterpart. By utilizing genomic DNA as template, we amplified the whole CSN1S1 gene plus 1972/3 nucleotides of the 5' region plus 610 nucleotides of the 3' region of the goat CSN1S1 N and CSN1S1 F alleles. Comparison of sequences of the N, F and A CSN1S1 alleles showed a total of 118 polymorphic sites. In particular, both the N and the F alleles are characterized by a deletion of the cytosine at the 23rd nucleotide of the 9th exon. The resulting one-nucleotide frameshift determines a premature stop codon (TGA, nucleotides 17-19 of the 12th exon). On the basis of the information so far available, it seems reasonable to hypothesize that the CSN1S1 N allele might be originated by interallelic recombination events. Comparison of transcripts produced by the N and F alleles shows a remarkable variability in alternative splicing events which concern, even though with different percentage ratios, mainly the lack of the 9th exon, the deletion of the last 5 nucleotides of the 9th exon and the contemporary deletion of exons 10 and 11.

Mass spectrometric approach for the analysis of food proteins

In the study of food proteins, the need for accurate protein structural analysis has been acknowledged because of the fact that nucleotide sequencing alone is of limited analytical value if not combined with relevant information regarding the specific protein expressed and the occurrence of phosphorylation, glycosylation and disulphide bridges, and with the modification induced by the technological treatment. Mass spectrometry, whether used alone or to complement the traditional molecular-based techniques has become fundamental to the structural analysis of proteins. It is, moreover, virtually irreplaceable in determining post-translational modifications as conventional methods cannot deliver reliable data. What lies at the root of this methodological breakthrough is the combination of high-resolution separation techniques such as two-dimensional electrophoresis or capillary reverse- phase high-performance liquid chromatography with mass spectrometric analysis, what is termed "proteomic" analysis. Thus, it appears appropriate to state that the new mass spectrometric techniques have been established as a valuable and efficient tool for protein and peptide analysis in complex mixtures, like those from food matrices, enabling us therefore to provide accurate information on molecular weight and also to put forth a structural assessment at a low-picomole level of material. Thus, a series of alternative approaches have been developed based on advanced mass spectrometric analysis in conjunction with classic protein chemistry in order to provide an in-depth view of food protein structure. This review outlines several of these novel methodologies as they apply to structural characterization of food products.

Mass spectrometric characterisation of proteins in rennet and in chymosin-based milk-clotting preparations

The protein composition of natural rennet and of chromatographic and crystalline chymosin preparations has been defined by on-line reverse-phase high performance liquid chromatography/electrospray ionisation mass spectrometry (RP-HPLC/ESI-MS) and by tandem mass spectrometry (MS/MS). Natural rennet was found to consist of six chymosin species, corresponding to chymosin A and B genetic variants, each of which comprised a mixture of two other forms differing at theN-terminal end, with one being three residues longer, and the other two residues shorter, than the mature chymosin. Two main tissue proteins were also identified as lysozyme (isozyme 2 plus a novel isozyme labelled 4) and bovine serum albumin. In addition to the proteins, chymosin fragments 247-323 and 288-323 were consistently present in natural rennet. Conversely, chromatographic and crystalline chymosin preparations lacked bovine serum albumin and/or lysozyme, although they contained the same six chymosin species as natural rennet. Since these tissue-specific contaminating proteins each possess specific functions in terms of stabilising enzyme solutions and protecting proteins from proteolytic enzymes, oxidising agents and bacterial proliferation, the rennet may be considered as a functional enzyme preparation that is effectively and naturally adapted to the purposes of cheesemaking. In practice, the highly complex protein composition inherent to natural rennet provided the possibility to differentiate the natural product from other bovine chymosin-based milk-clotting preparations examined in this work.

Analysis of major ovine milk proteins by reversed-phase high-performance liquid chromatography and flow injection analysis with electrospray ionization mass spectrometry

Ovine milk proteins were analyzed both by coupling HPLC and electrospray ionization mass spectrometry (ESI-MS) and by flow injection analysis and ESI-MS detection after separation and collection of fractions from gel permeation chromatography. These methods resolved the four ovine caseins and whey proteins and made it possible to study the complexity of these proteins associated with genetic polymorphism, post-translational changes (phosphorylation and glycosylation) and the presence of multiple forms of proteins. The experimental molecular masses of ewe milk proteins were: 19,373 for kappa-casein 3P; 25,616 for alpha(s2)-casein 10P; 23,411 for alpha(s1)-casein C-8P; 23,750 for beta-casein 5P; 18,170 and 18,148 for beta-lactoglobulins A and B; 14,152 for alpha-lactalbumin A and 66,322 for serum albumin.

Alternative nonallelic deletion is constitutive of ruminant alpha(s1)-casein

Multiple forms of alpha(s1)-casein were identified in the four major ruminant species by structural characterization of the protein fraction. While alpha(s1)-casein phenotypes were constituted by a mixture of at least seven molecular forms in ovine and caprine species, there were only two forms in bovine and water buffalo species. In ovine and caprine forms the main component corresponded to the 199-residue-long form, and the deleted proteins differed from the complete one by the absence of peptides 141-148, 110-117, or Gln78, or a combination of such deletions. The deleted segments corresponded to the sequence regions encoded by exons 13 and 16, and by the first triplet of exon 11 (CAG), suggesting that the occurrence of the short protein forms is due to alternative skipping, as previously demonstrated for some caprine and ovine phenotypes. The alternative deletion of Gln78 in alpha(s1)-casein, the only form common to the milk of all the species examined and located in a sequence region joining the polar phosphorylation cluster and the hydrophobic C-terminal domain of the protein, may play a functional role in the stabilization of the milk micelle structure.