Milk protein genetic variants and isoforms identified in bovine milk representing extremes in coagulation properties

Jensen, H. B., Holland, J. W., Poulsen, N. A. and Larsen, L. B. (2012) Milk protein genetic variants and isoforms identified in bovine milk representing extremes in coagulation properties. Journal of Dairy Science, 95 6: 2891-2903. doi:10.3168/jds.2012-5346

Author Jensen, H. B.
Holland, J. W.
Poulsen, N. A.
Larsen, L. B.
Title Milk protein genetic variants and isoforms identified in bovine milk representing extremes in coagulation properties
Journal name Journal of Dairy Science   Check publisher's open access policy
ISSN 0022-0302
Publication date 2012-06
Sub-type Article (original research)
DOI 10.3168/jds.2012-5346
Volume 95
Issue 6
Start page 2891
End page 2903
Total pages 13
Place of publication New York, NY, United States
Publisher Elsevier
Collection year 2013
Language eng
Formatted abstract
A gel-based proteomic approach consisting of 2-dimensional gel electrophoresis coupled with mass spectrometry was applied for detailed protein characterization of a subset of individual milk samples with extreme rennet coagulation properties. A milk subset with either good or poor coagulation abilities was selected from 892 Danish Holstein-Friesian and Jersey cows. Screening of genetic variants of the major milk proteins resulted in the identification of common genetic variants of β-casein (CN; A 1, A 2, B), κ-CN (A, B), and β-lactoglobulin (LG; A, B), as well as a low frequency variant, κ-CN variant E, and variants not previously reported in Danish breeds (i.e., β-CN variant I and β-LG variant C). Clear differences in the frequencies of the identified genetic variants were evident between breeds and, to some extent, between coagulation groups within breeds, indicating that an underlying genetic variation of the major milk proteins affects the overall milk coagulation ability. In milk with good coagulation ability, a high prevalence of the B variants of all 3 analyzed proteins were identified, whereas poorly coagulating milk was associated with the β-CN variant A 2, κ-CN variant A or E, and β-LG variant A or C. The β-CN variant I was identified in milk with both good and poor coagulation ability, a variant that has not usually been discriminated from β-CN variant A 2 in other studied cow populations. Additionally, a detailed characterization of κ-CN isoforms was conducted. Six κ-CN isoforms varying in phosphorylation and glycosylation levels from each of the genetic variants of κ-CN were separated and identified, along with an unmodified κ-CN form at low abundance. Relative quantification showed that around 95% of total κ-CN was phosphorylated with 1 or 2 phosphates attached, whereas approximately 35% of the identified κ-CN was glycosylated with 1 to 3 tetrasaccharides. Comparing isoforms from individual samples, we found a very consistent κ-CN isoform pattern, with only minor differences in relation to breed, κ-CN genetic variant, and milk coagulation ability.
Keyword Rennet coagulation
Milk protein genetic variant
Posttranslational modification
Mass spectrometry
Q-Index Code C1
Q-Index Status Confirmed Code
Institutional Status UQ
Additional Notes Available online: 18 May 2012.

Document type: Journal Article
Sub-type: Article (original research)
Collections: Official 2013 Collection
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