title: Parotid secretory protein binds phosphatidylinositol (3,4) bisphosphate.
abstract: Molecular interactions that direct trafficking of secreted proteins are not well-described in salivary glands. Here, we report that the soluble cargo protein Parotid Secretory Protein (PSP) is bound to the membranes of secretory granules isolated from rat parotids. This is apparently due to specific interaction with phosphatidylinositol phosphates (PtdInsP). PSP binds PtdIns(3,4)P(2), 10-fold greater than PtdIns(3,5)P(2) or PtdIns(4)P, and does not bind PtdIns(3)P or PtdIns(5)P. Human PSP synthesized in vitro also binds PtdIns(3,4)P(2). Bacterially expressed rat PSP binds PtdIns(3,4)P(2) with a K(d) of 2.4 x 10(-11) M. Other major secretory proteins (amylase, proline-rich protein) are not bound to isolated granule membranes and do not bind phosphatidylinositol phosphates. Immunofluorescence shows PtdIns(3,4)P(2) at the secretory granules, and fluorescent PtdIns(3,4)P(2) can flip from the outer leaflet to the inner leaflet of the membrane. Binding of PSP to PtdInsPs may contribute to sorting during the formation of the secretory granules, or sorting by retention during maturation of the granules.
authors.affiliation: Center for Oral Health and Systemic Disease, School of Dentistry, 501 South Preston Street, Room 331, University of Louisville, Louisville, KY 40202, USA.
authors.forename: S G
authors.initials: SG
authors.lastname: Venkatesh
authors.forename: D
authors.initials: D
authors.lastname: Goyal
authors.forename: A L
authors.initials: AL
authors.lastname: Carenbauer
authors.forename: D S
authors.initials: DS
authors.lastname: Darling
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D015153:Blotting, Western; D006801:Humans; D007425:Intracellular Membranes / Q000378:metabolism; D008297:Male; D010306:Parotid Gland / Q000378:metabolism*; D018129:Phosphatidylinositol Phosphates / Q000378:metabolism*; D040081:Protein Array Analysis; D011485:Protein Binding; D021381:Protein Transport; D051381:Rats; D017207:Rats, Sprague-Dawley; D012471:Salivary Proteins and Peptides / Q000378:metabolism*; D022142:Secretory Vesicles / Q000378:metabolism; D018709:Statistics, Nonparametric
chemical_list: C511598:Bpifa2 protein, rat; D018129:Phosphatidylinositol Phosphates; D012471:Salivary Proteins and Peptides; C060980:phosphatidylinositol 3,4-diphosphate