Analysis of MAGP1 interaction with selected plasma proteins. MAGP1's ability to interact with plasma proteins was assayed by ligand blot (A) and coimmunoprecipitation (B). (A) Lanes: FN indicates fibronectin; VWF, von Willebrand factor; Fb, fibrinogen; and STD, molecular weight standards. The left side of the panel is a Coomassie blue–stained gel (± DTT) of the separated proteins. The right side shows a ligand blot of the same proteins after transfer to nitrocellulose, incubation with MAGP1, and bound MAGP1 detected with an antibody to MAGP1 after extensive washing to remove unbound protein. (B) SDS-PAGE autoradiogram showing coprecipitation of [¹²⁵I]-labeled plasma proteins and V5-tagged MAGP1. Lanes: 1, fibronectin with V5 antibody only (negative control); 2, fibronectin coprecipitated with MAGP1-V5 using V5 antibody; 3, fibronectin coprecipitated with MAGP1-V5 as in lane 2, but in the presence of 10-fold excess unlabeled fibronectin; 4, fibrinogen with V5 antibody; 5, fibrinogen coprecipitated with MAGP1-V5 using V5 antibody; 6, fibrinogen coprecipitated with MAGP1-V5 as in lane 5, but in the presence of 10-fold excess unlabeled fibrinogen; 7, von Willebrand factor with V5 antibody; 8, von Willebrand factor coprecipitated with MAGP1-V5 using V5 antibody; and 9, von Willebrand factor coprecipitated with MAGP1-V5 as in lane 8, but in the presence of 10-fold excess von Willebrand factor. Vertical lines have been inserted to indicate repositioned gel lanes.