Lysozyme and alpha-lactalbumin from the milk of a marsupial, the common brush-tailed possum (Trichosurus vulpecula).

Lysozyme and alpha-lactalbumin have been identified using N-terminal sequence analysis of whey proteins from the common brush-tailed possum, Trichosurus vulpecula after separation by two-dimensional denaturing electrophoresis. Both proteins were purified from pooled possum milk using ion exchange chromatography and gave mass values of 14,896 and 13,985 Da respectively by MALDI-TOF mass spectrometry. Clones containing the full coding sequences of the genes for both proteins were isolated from a possum mammary cDNA library and the DNA sequence of the coding region determined. The inferred protein sequences were used in phylogenetic analysis of both protein classes. These showed that the T. vulpecula alpha-lactalbumin, along with other marsupial alpha-lactalbumins, formed a family distinct from the eutherian alpha-lactalbumins and the alpha-lactalbumin of a monotreme, the platypus, consistent with the separate evolution of the marsupials. By contrast the T. vulpecula lysozyme was shown to be similar to the ruminant stomach lysozymes and primate lysozymes and quite distinct from the Ca2+-binding lysozymes found in the milk of the echidna and horse.