title: Bovine PAS-6/7 binds alpha v beta 5 integrins and anionic phospholipids through two domains.
abstract: Bovine milk fat globule membranes are a rich source of glycoproteins PAS-6 (52 kDa) and PAS-7 (47 kDa). They are glycosylation variants sharing a common polypeptide core. The PAS-6/7 protein consists of two EGF-like domains and a tandem repeated structure with a high degree of similarity to the C1 and C2 domains found in blood-clotting factors V and VIII. The second EGF-like domain contains an RGD cell adhesion sequence with the possibility of binding integrins, while the C-terminal end of the C2-like domain contains a probable amphipathic alpha-helix. Using a PAS-6/7 column, bovine alpha v beta 5 integrin was purified from mammary gland tissue by affinity chromatography and characterized by Western blotting and N-terminal sequencing. The interaction between PAS-6/7 and the alpha v beta 5 integrin was shown to be RGD dependent. Lipid binding assays showed that PAS-6/7 binds to surfaces of phosphatidylserine, -inositol, and -glycerol, and their precursor, phosphatidic acid, but not phosphatidylcholine. Furthermore, PAS-6/7 displayed the highest affinity toward a total lipid fraction derived from the milk fat globule membrane as compared to pure phospholipids. Using Western blotting technique, PAS-6/7 was shown to be widely expressed in a number of tissues. These results show that PAS-6/7 is a common protein which can bind to membranes by two distinct mechanisms, one through affinity to integrin alpha v beta 5 and another by direct binding to phospholipids.
authors.affiliation: Protein Chemistry Laboratory, University of Aarhus, Denmark.
authors.forename: M H
authors.initials: MH
authors.lastname: Andersen
authors.forename: L
authors.initials: L
authors.lastname: Berglund
authors.forename: J T
authors.initials: JT
authors.lastname: Rasmussen
authors.forename: T E
authors.initials: TE
authors.lastname: Petersen
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000838:Anions; D002417:Cattle; D005260:Female; D016023:Integrins / Q000302:isolation & purification / Q000378:metabolism*; D008024:Ligands; D008562:Membrane Glycoproteins / Q000737:chemistry* / Q000378:metabolism*; D008894:Milk Proteins / Q000737:chemistry* / Q000378:metabolism*; D008969:Molecular Sequence Data; D010743:Phospholipids / Q000378:metabolism*; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D019030:Receptors, Vitronectin; D014018:Tissue Distribution
chemical_list: D000838:Anions; D016023:Integrins; D008024:Ligands; D008562:Membrane Glycoproteins; D008894:Milk Proteins; C106215:PAS-6-7 glycoprotein, Bos taurus; D010743:Phospholipids; D019030:Receptors, Vitronectin; C064660:integrin alphaVbeta5