Phylogenetic analysis of three lipocalin-like proteins present in the milk of Trichosurus vulpecula (Phalangeridae, Marsupialia)

Three proteins have been identified in the milk of the common brush tail possum, Trichosurus vulpecula that from sequence analysis are members of the lipocalin family. They include beta-lactoglobulin, which appears to have two forms; a homologue to the late lactation protein found in tammar, Macropus eugenii; milk; and a novel protein termed trichosurin. Whereas beta-lactoglobulin and trichosurin are both expressed throughout lactation, the late-lactation protein is not detected in samples taken before days 100-110 of lactation. The cDNAs encoding each of these proteins have been isolated from cDNA libraries prepared using possum mammary mRNA and sequenced. Phylogenetic analysis showed that the T. vulpecula beta-lactoglobulin, along with two other macropod beta-lactoglobulins, forms a subclass of beta-lactoglobulins distinct from those for eutherian mammals; both marsupial late-lactation proteins appear to have similarities to a family of odorant-binding proteins, whereas trichosurin has similarities to the major urinary proteins of rodents.