Figure 1.
Figure 1. NCAM IgI-IgII structure and homophilic binding. a,
Stereo view of the C trace
of the two N-terminal immunoglobulin (Ig) domains of NCAM
IgI-IgII. Every 10^th residue is labeled. Both domains belong to
the I-type subfamily of Ig domains, and are tightly connected by
a linker region of only two amino acids (Lys 98 and Leu 99) due
to a long G strand in IgI. IgI consists of nine -strands
whereas IgII contains only eight. The tilt angle between the
domains is very small and this leads to an extended overall
conformation. b,c, Ribbon diagram of the quaternary structure of
the NCAM IgI-IgII dimer, using the A -B dimer as representative.
b, Two IgI-IgII molecules form a cross shaped homodimer.
Molecule A is shown in blue and molecule B in magenta with their
individual domains labeled IgI and IgII. Two nearly symmetric
interactions are formed in the dimer -- the residues forming
interactions between IgI of molecule A and IgII of molecule B
are virtually identical to those between IgII of molecule A and
IgI of molecule B. IgII contains the putative heparin binding
site of NCAM, and the loop bearing this sequence is shown in
green. c, The dimer is rotated 90° around the vertical axis
relative to the view in (b). This view shows the two salt bridge
interactions between Glu 16 and Lys 98 in the linker region of
molecule A and the corresponding residues in molecule B. The
center of symmetry in the linker region is clear in this view.
The Glu and Lys residues are colored according to atom types:
carbon, green; nitrogen, blue and oxygen, red. d, Schematic
representation of the mechanism of homophilic cell -cell
adhesion mediated by NCAM based on the crystal structure. The
cell surfaces are shown in black with NCAM protruding from them.
The NCAM monomers, shown on the left, mediate adhesion by
dimerization of IgI and IgII from opposite cells, as shown on
the right. The two membrane proximal F3 domains are shown as
green squares, and domains IgIII to IgV are depicted as pink and
blue ovals, as the three-dimensional structures of these domains
are not yet known. According to electron microscopy experiments
there is a hinge region near IgV19, 22.
The above figure is reprinted
by permission from Macmillan Publishers Ltd:
Nat Struct Biol
(2000,
7,
389-393)
copyright 2000.
trace
of the two N-terminal immunoglobulin (Ig) domains of NCAM
IgI-IgII. Every 10^th residue is labeled. Both domains belong to
the I-type subfamily of Ig domains, and are tightly connected by
a linker region of only two amino acids (Lys 98 and Leu 99) due
to a long G strand in IgI. IgI consists of nine 
-strands
whereas IgII contains only eight. The tilt angle between the
domains is very small and this leads to an extended overall
conformation. b,c, Ribbon diagram of the quaternary structure of
the NCAM IgI-IgII dimer, using the A -B dimer as representative.
b, Two IgI-IgII molecules form a cross shaped homodimer.
Molecule A is shown in blue and molecule B in magenta with their
individual domains labeled IgI and IgII. Two nearly symmetric
interactions are formed in the dimer -- the residues forming
interactions between IgI of molecule A and IgII of molecule B
are virtually identical to those between IgII of molecule A and
IgI of molecule B. IgII contains the putative heparin binding
site of NCAM, and the loop bearing this sequence is shown in
green. c, The dimer is rotated 90° around the vertical axis
relative to the view in (b). This view shows the two salt bridge
interactions between Glu 16 and Lys 98 in the linker region of
molecule A and the corresponding residues in molecule B. The
center of symmetry in the linker region is clear in this view.
The Glu and Lys residues are colored according to atom types:
carbon, green; nitrogen, blue and oxygen, red. d, Schematic
representation of the mechanism of homophilic cell -cell
adhesion mediated by NCAM based on the crystal structure. The
cell surfaces are shown in black with NCAM protruding from them.
The NCAM monomers, shown on the left, mediate adhesion by
dimerization of IgI and IgII from opposite cells, as shown on
the right. The two membrane proximal F3 domains are shown as
green squares, and domains IgIII to IgV are depicted as pink and
blue ovals, as the three-dimensional structures of these domains
are not yet known. According to electron microscopy experiments
there is a hinge region near IgV19, 22.