Fig. 5. Aggrecan binding to TN-R FNIII domains 4-A blocks the interaction between TN-R and contactin 1. COS7 cells expressing contactin 1 on their surface were incubated with contactin 1-coated microspheres in the presence of TN-R (10 µg/ml) (A) together with aggrecan (20 µg/ml) (B-D), Fab fragments of pAb to TN-R FNIII domains 4-A (500 µg/ml) (C) and TN-R fragment FNIII domains 4-A (100 µg/ml) (D). Double fluorescence images of contactin 1 expression (left) and contactin 1-coated microsphere binding (right) are shown as described in Fig. 4. Bar, 100 µm. The blocking effect of aggrecan on TN-R bridge formation between contactin 1 polypeptides depends on the interaction of aggrecan with TN-R FNIII domains 4-A.