Concanavalin A distorts the b -GlcNAc-(1 (cid:1) 2)-Man linkage of b -GlcNAc-(1 (cid:1) 2)- a -Man-(1 (cid:1) 3)-[ b -GlcNAc-(1 (cid:1) 2)- a -Man-(1 (cid:1) 6)]-Man upon binding