Characterization and Genotyping of the Caprine κ-Casein Variants

Abstract

Kappa-Casein (kappa-CN) is the milk protein that determines the size and specific function of milk micelles, and its cleavage by chymosin is responsible for milk coagulation. We have previously detected and characterized four variants of the goat kappa-CN in Spanish, French, and Italian breeds by screening the major part of the coding region in exon 4. Here we have sequenced and analyzed the full coding region of the kappa-CN gene which includes exons 3 and 4. No additional mutations were found, with exception of a single nucleotide substitution in exon 3, which had no amino acid change. However, the analysis of the association between the different mutations resulted in two new variants designated kappa-CN F and G. The novel variants are present in the Italian breeds Teramana, Girgentana, and Sarda (variant F). A protocol for rapid simultaneous genotyping of all known kappa-CN variants using the primer extension method was described, and a total of 210 animals from nine European breeds were genotyped. Alleles A and B are the most frequent variants occurring in the majority of breeds with highest prevalence of the B variant, except for the Canaria breed where the A allele is more frequent. Sequence data suggest that the F variant is the original type of caprine kappa-CN, other alleles being derived from this type following two different trunks by successive mutations.

Casein Haplotype Structure in Five Italian Goat Breeds

“…A phylogeny for CSN3 was proposed by Yahyaoui et al (2003) and by Jann et al (2004). Apart from the conflicting nomenclature, both papers agree that CSN3*A appeared later in the evolutionary pathway and that 2 different lineages occurred.…”

“…Frequencies ranged from 0.596 (Vallesana) to 0.776 (Garganica). The allele was referred to as B in Yahyaoui et al (2003). It will be important to find an international agreement on CSN3 nomenclature in the future.…”

“…A total of 13 polymorphic sites were identified in the domestic goat (Jann et al, 2004), allowing the identification of 14 alleles corresponding to 11 protein variants, if taking into account the Capra pyrenaica variant (Yahyaoui et al, 2001), which was later observed in domestic goat breeds (Yahyaoui et al, 2003). Recently, 2 more polymorphisms were demonstrated by PCR-single strand conformational polymorphism (PCR-SSCP) analysis (Chessa et al, 2003), but they are not yet characterized.…”

“…Since the discovery of 2 caprine k-casein variants identifiable by isoelectrofocusing (IEF) (Di Luccia et al, 1990) and successively confirmed both at the protein and DNA level by Caroli et al (2001), further CSN3 polymorphisms were detected by DNA analysis (Yahyaoui et al, 2001;Angiolillo et al, 2002;Yahyaoui et al, 2003;Jann et al, 2004). A total of 13 polymorphic sites were identified in the domestic goat (Jann et al, 2004), allowing the identification of 14 alleles corresponding to 11 protein variants, if taking into account the Capra pyrenaica variant (Yahyaoui et al, 2001), which was later observed in domestic goat breeds (Yahyaoui et al, 2003).…”

Protein composition and polymorphism in the milk of Skopelos goats

“…The presentation in Table VI is according to the most recent nomenclature, proposed by Jann et al [20], in which the former B variant [50] has been renamed as D and vice versa. The goat κ-cn variants were not separated on the C4 column and on the IEF gels.…”