|
Figure 3.
FIG. 3. Lactose and N-acetyllactosamine binding to the
lectin module of LSL. A, structure of the Lac molecule bound to
the  -motif of LSL. B,
three-dimensional structure of LacNAc bound to the -motif
of LSL. The models show the F[o] - F[c] electron density maps
contoured at 2.5  around the Lac molecule
initially calculated without including the disaccharide. C,
LacNAc bound to the  -motif. The F[o] - F[c]
electron density map contoured at 3 calculated without
including the disaccharide is shown in blue around the bound
carbohydrate. Broken lines indicate hydrogen bonds between sugar
and protein residues. Color coding of secondary structure
elements:  -motif, blue; -motif,
red, -motif, green. D,
molecular surface of the -trefoil scaffold, with
the LacNAc molecules (as stick models) bound to the - and
-sites. The surface is
colored according to the electrostatic potential, blue for
positive and red for negative. E, structure of Lac bound to one
binding site in ricin B-chain (Protein Data Bank code 2AAI [PDB]
; Ref. 40). A-C were prepared with MOLSCRIPT (54) and RASTER3D
(53); the molecular surface was built with the program GRASP
(55).
|
