Polymorphism at donkey β-lactoglobulin II locus: identification and characterization of a new genetic variant with a very low expression
In the last years, donkey milk had evidenced a renewed interest as a potential functional food and a breast milk substitute. In this light, the study of the protein composition assumes an important role. In particular, β-lactoglobulin (β-LG), which is considered as one of the main allergenic milk protein, in donkey species consists of two molecular forms, namely β-LG I and β-LG II. In the present research, a genetic analysis coupled with a proteomic approach showed the presence of a new allele, here named F, which is apparently associated with a null or a severely reduced expression of β-LG II protein. The new β-LG II F genetic variant shows a theoretical average mass (Mav) of 18,310.64 Da, a value practically corresponding with that of the variant D (∆mass < 0.07 Da), but differs from β-LG II D for two amino acid substitutions: Thr100 (variant F) → Ala100 (variant D) and Thr118 (variant F) → Met118 (variant D). Proteomic investigation of the whey protein fraction of an individual milk sample, homozygous FF at β-LG II locus, allowed to identify, as very minor component, the new β-LG II F genetic variant. By MS/MS analysis of enzymatic digests, the sequence of the β-LG II F was characterized, and the predicted genomic data confirmed.
KeywordsPolymorphism LGB2 gene Donkey milk Allergy Mass spectrometry SNPs
This work was supported by grants from PO FERS 2007/13 4.1.2.A, project “Piattaforma regionale di ricerca translazionale per la salute”, CUP B65E12000570008. The authors gratefully acknowledge the Bio-Nanotech Research and Innovation Tower (BRIT; PON project financed by the Italian Ministry for Education, University and Research, MIUR) for the availability of the Orbitrap Fusion mass spectrometer.
Compliance with ethical standards
Conflict of interest
The authors declare that there are no conflicts of interest.
All applicable international, national, and/or institutional guidelines for the care and use of animals were followed.
- Chianese L, De Simone C, Ferranti P, Mauriello R, Costanzo A, Quarto M, Garro G, Picariello G, Mamone G, Ramunno L (2013) Occurrence of qualitative and quantitative polymorphism at donkey betalactoglobulin II locus. Food Res Int 54:1273–1279. https://doi.org/10.1016/j.foodres.2012.11.005 CrossRefGoogle Scholar
- European Commission. 2010. Directive 2010/63/EU of the European Parliament and of the Council of 22 September 2010 on the protection of animals used for scientific purposes. In: Official Journal of the European Union. L 276/33. 20.10.2010Google Scholar
- Godovac-Zimmermann J, Conti A, James L, Napolitano L (1988) Microanalysis of the amino-acid sequence of monomeric beta-lactoglobulin I from donkey (Equus asinus) milk. Biol Chem H-S 369:171–179Google Scholar
- Godovac-Zimmermann J, Conti A, Sheil M, Napolitano L (1990) Covalent structure of the minor monomeric β-lactoglobulin II component from donkey milk. Biol Chem H-S 371:871–879Google Scholar
- Mansueto P, Iacono G, Taormina G, Seidita A, D’Alcamo A, Adragna F, Randazzo G, Carta Rini G, Carroccio A (2013) Ass’s milk in allergy to cow’s milk protein: a review. Acta Med Mediterr 29:153–160Google Scholar
- Marletta D, Tidona F, Bordonaro S (2016) Donkey milk proteins: digestibility and nutritional significance. In: “Milk Proteins—From Structure to Biological Properties and Health Aspects” pp 199–209. https://doi.org/10.5772/62597
- Swar MO (2011) Donkey milk-based formula: a substitute for patients with cow’s milk protein allergy. Sudan J Paediatr 11:21–24Google Scholar