New genetic variants identified in donkey's milk whey proteins.

Novel genetic variants for donkey milk lysozyme and beta-lactoglobulins I and II have been identified by the combined use of peptide mass mapping and sequencing by tandem mass spectrometry in association with database searching. The novel donkey lysozyme variant designated as lysozyme B (Mr 14,631 Da) differed in three amino acid exchanges, N49 --> D, Y52 --> S, and S61 --> N, from the previously published sequence. Three novel genetic variants for donkey beta-lactoglobulins were identified. One of them is a type beta-lactoglobulin I with three amino acid exchanges at E36 --> S, S97 --> T, and V150 --> I (beta-lactoglobulin I B, Mr 18,510 Da). The two others are type beta-lactoglobulins II with two amino acid exchanges at C110 --> P and M118--> T (beta-lactoglobulin II B, Mr 18,227 Da) and with three amino acid exchanges at D96 --> E, C110 --> P, and M118 -->T (beta-lactoglobulin II C, Mr 18,241 Da). All these primary structures are closely related to those of homologous proteins in horse milk (percent identity >96%).