Casein composition and differential translational efficiency of casein transcripts in donkey's milk

Abstract

The amount of the four caseins (αs1, αs2, β and κ-CN) in donkey milk was evaluated by Urea-PAGE analysis at pH 8.6, followed by immuno-detection with polyclonal antibodies, coupled to densitometric analysis. The results showed the percentage of each casein in decreasing order: β (54.28) > αs1 (35.59) > αs2 (7.19) > κ-CN (2.79). The mRNA quantification of donkey casein transcripts, carried out by RT-qPCR, showed that the average percentage of corresponding gene transcripts (CSN2, CSN1S1, CSN1S2 I and CSN3) was 70.85, 6.28, 14.23 and 8.65, respectively. The observed translation efficiency, assessed as percentage of single milk casein fraction out of single percentage of transcript, was 0.76, 5.66, 0.50 and 0.32, respectively. The analysis of the sequences flanking the start codon, the codon usage frequencies and the coding sequence length might explain, at least in part, the differential transcriptional and translational rate observed among the casein transcripts.

Milk Products from Minor Dairy Species: A Review

“…In particular, Cn/Wp is less than one third with respect to cow milk; the casein micelle is larger and contains a different pattern of single fractions, with β-casein being the most abundant and k-casein present in trace amounts ( Table 1 ). However, recent research is supplying evidence of a wide genetic variability in synthetizing the αs1 fraction, suggesting that the casein pattern can present wide variations from individual to individual [ 20 , 21 , 22 ]. The scarce presence of k-casein is responsible of higher average size of the micelle and different mechanisms for micelle stability with respect to cow milk [ 23 , 24 , 25 ]; these characteristics, together with the low total casein content, are probably involved in the poor coagulation properties.…”

Donkey milk composition and its therapeutic applications

“…The lower casein concentration in donkey's milk (about 50% of total protein) compared with bovine milk (80% of total protein) (Zicker and Lonnerdal 1994) and the relevant percentage of essential amino-acids make this milk a new dietetic food and a promising breast milk substitute (Guo et al 2007). A more recent study on donkey milk has revealed the percentage of four caseins (αs1, αs2, β and κ-CN) in decreasing order: β (54.28) > αs1 (35.59) > αs2 (7.19) > κ-CN (2.79) as evaluated by Urea-PAGE analysis at pH 8.6, followed by immuno-detection with polyclonal antibodies, coupled to densitometric analysis (Cosenza et al 2019).…”