New genetic variants identified in donkey's milk whey proteins

Novel genetic variants for donkey milk lysozyme and beta-lactoglobulins I a nd II have been identified by the combined use of peptide mass mapping and sequencing by tandem mass spectrometry in association with database searchi ng. The novel donkey lysozyme variant designated as lysozyme B (Mr 14,631 D a) differed in three amino acid exchanges, N-49 --> D, Y-52 --> S, and S-61 --> N, from the previously published sequence. Three novel genetic variant s for donkey beta-lactoglobulins were identified. One of them is a type bet a-lactoglobulin I with three amino acid exchanges at E-36 --> S, S-97 --> T , and V-150 --> I (beta-lactoglobulin I B, Mr 18,510 Da). The two others ar e type beta-lactoglobulins II with two amino acid exchanges at C-110 --> P and M-118 --> T (beta-lactoglobulin II B, Mr 18,227 Da) and with three amin o acid exchanges at D-96 --> E, C-110 --> P, and M-118 --> T (beta-lactoglo bulin II C, Mr 18,241 Da). AU these primary structures are closely related to those of homologous proteins in horse milk (percent identity >96%).