Identification, characterisation and cDNA cloning of two caseins from the common brushtail possum (Trichosurus vulpecula)

Two major caseins have been isolated from the milk of the common brushtaile d possum (Trichosurus vulpecula). These have been identified as alpha- and beta-casein on the basis of the similarity of their N-terminal sequences to those of the caseins of another marsupial (Macropus eugenii). Both protein s appear to exist in multiple forms. Possum alpha-casein is glycosylated ma inly in the form of sialic acid residues and was shown by electrospray mass spectrometry to have multiply phosphorylated forms of three families with molecular masses 22 700 and 23 200 Da that may represent genetic variants. Two-dimensional electrophoresis showed that beta-casein exists as a complex of five or six proteins of identical N-terminal sequence but differing pi. Electrospray mass spectrometry indicated that the beta-caseins also are mu ltiply phosphorylated with masses between 32 300 and 32 600 Da. A subfamily with mass values 1530 greater was also detected. The patterns were not aff ected by stage of lactation and quantitative analysis of two-dimensional ge ls of whole milk shows that alpha- and beta-caseins are present at a consta nt ratio throughout lactation. cDNA clones for the possum alpha- and beta-c aseins have been isolated from an early lactation mammary cDNA library and sequenced. (C) 1999 Elsevier Science B.V. All rights reserved.