GPI-ANCHORED COMPLEMENT REGULATORY PROTEINS IN SEMINAL PLASMA - AN ANALYSIS OF THEIR PHYSICAL CONDITION AND THE MECHANISMS OF THEIR BINDINGTO EXOGENOUS CELLS

We analyzed and compared the properties of three glycosylphosphatidyli nositol (GPI)-anchored proteins, CD59, CD55 (both C regulators), and C Dw52, and of the transmembrane C regulator CD46 in seminal plasma (SP) . We demonstrated previously that anchor-intact SP CD59 is present on the membranes of vesicles (prostasomes) and that cells acquire this pr otein during incubation with SP, We now report that this acquisition i s due partly to adherence of prostasomes to cells and partly to a seco nd mechanism which may involve micellar intermediates, Using fluoresce nt labeling, ultracentrifugation, and density gradient centrifugation, virtually all CD46 was present on prostasomes whereas CD59, CD55, and CDw52 were also detected in a form which remained in the 200,000 g su pernatant and equilibrated at higher density than prostasomes in gradi ents, All three GPI-linked proteins eluted at high molecular mass duri ng size exclusion chromatography of this nonprostasome fraction, As do cumented by videomicroscopy and biochemical analysis, cells acquired n ew copies of the GPI-linked proteins during incubation with the nonpro stasome fraction as well as with prostasomes, These data demonstrate t he presence in SP of a stable population of membrane-free, GPI-linked proteins available for transfer to cells, Binding of these proteins to spermatozoa and pathogens in SP may confer new properties on their me mbranes including increased resistance to C attack. Finally, our data raise the possibility that lipid-associated GPI-linked proteins may be suitable for therapeutic applications.