HUMAN FACTOR-IX BINDS TO SPECIFIC SITES ON THE COLLAGENOUS DOMAIN OF COLLAGEN-IV

The primary region of factor IX that mediates binding to bovine aortic endothelial cells resides in residues 3-11 of the N-terminal region k nown as the Gla domain, Recently, it was proposed that the observed bi nding to endothelial cells is actually a measure of the interaction be tween factor IX and collagen IV (Cheung, W. F., van den Born, J., Kuhn , K., Kjellen, L., Hudson, B. G., and Stafford, D. W. (1996) Proc, Nat l, Acad, Sci, U. S. A. 93, 11068-11073), To confirm that factor M bind s to collagen IV and to examine the specificity of this interaction, w e used scanning force microscopy to examine factor M binding to collag en IV, We imaged collagen IV in the presence and the absence of factor IX and observed specific interactions between factor IX and collagen IV, Our results demonstrate that factor IX binds to collagen IV at spe cific sites in the collagenous domain similar to 98 and similar to 50 nm from the C-terminal pepsin-cleaved end.