β-Lactoglobulin Identified in Marsupial Milk. The Primary Structure, Binding Site and possible Function of β-Lactoglobulin from Eastern Grey Kangaroo(Macropus giganteus)

Abstract

0-Lactoglobulin has been isolated in the milk of the Eastern Grey Kangaroo (Macropus giganteus). This is the first time this protein has been reported to be in the milk of marsupials.The complete amino-acid sequence has been determined by spinning cup and pulsed liquid phase microsequencing of the protein and peptides after enzymatic or cyanogen bromide cleavages.The 155-residue protein is the shortest (3-lactoglobulin so far sequenced. When the kangaroo protein is included in a comparison of the members of the 0-lactoglobulin family, the percentage of residues common to all members is reduced from 33% to 13%. Despite the large number of accumulated amino-acid exchanges the protein exists as a dimer and shows higher homology to the usually very conservative dimeric, ruminant 0-lactoglobulins than to the monomeric protein from monogastrics. Half-cystine residues that form disulphide bridges are conserved. The Eastern Grey Kangaroo 0-lactoglobulin possesses significant homology in several characteristic segments thought to be important for a functional trait common to the j3-lactoglobulin family and retinol-binding proteins. Structural similarity to the retinol-binding protein is indicated by 22% of identical residues. Homology to the (3-lactoglobulins and retinolbinding proteins, the binding site and possible function based on comparative structural studies are discussed. Nachweis von ß-Lactoglobulin in Känguruhmilch. Primärstruktur, Bindungsstellen und mögliche Funktion des ß-Lactoglobulins des grauen Riesenkänguruhs (Macropus giganteus)Zusammenfassung: In der Milch des grauen Riesenkänguruh (Macropus giganteus) wurde erstmals ß-Lactoglobulin nachgewiesen und daraus isoliert. Die vollständige Aminosäuresequenz wurde mit automatischer Mikrosequenzierung (spinning cup und pulsed liquid phase) der Kette und der Peptide nach enzymatischer oder Bromcyanspaltung bestimmt. Es ist mit 155 Resten das kürzeste aller bisher sequenzierten ß-Lactoglobuline. Die Einbeziehung dieses ß-Lactoglobulins in den Vergleich vermindert die Homologie innerhalb dieser Proteinfamilie von 33% auf 13% identische Positionen. Trotz der vielen Aminosäureaustausche liegt das Protein als Dimeres vor und zeigt eine größere Homologie zu den sehr konservativen dimeren ß-Lactoglobulinen der Wiederkäuer, als zu den Monomeren der Nichtwiederkäuer. Die Positionen der disulfidbildenden Cysteine sind in der Struktur konserviert. Im ß-Lactoglobulin des grauen Riesenkängu-ruhs findet man signifikante Homologien in

Phylogenetic Analysis of Three Lipocalin-Like Proteins Present in the Milk of Trichosurus vulpecula (Phalangeridae, Marsupialia)

“…It is also found in the milk of nonruminant eutherians and has been identified in the milk of two macropod marsupials, Macropus giganteus, the eastern grey kangaroo (Godovac-Zimmermann and Shaw 1987), and Macropus eugenii, the tammar wallaby (Collet et al 1991). ␤-Lactoglobulin is thought to transport retinol and/or fatty acids (Godovac-Zimmermann 1988;Flower 1996).…”