Biomedical Engineering Reference
In-Depth Information
cluding fibronectin (FN), laminin (LN), and type I collagen (COL-I) [8].
In addition, several integrins bind to Ig-superfamily counterreceptors (e.g.,
VCAM, ICAM) to mediate cell-cell adhesion. Integrins are
αβ
heterodimers;
18
subunits have been identified to dimerize into 24 distinct re-
ceptors. Most integrins are expressed on a wide variety of cell types, and
most cells express several integrin receptors. However, some subclasses are
only expressed in particular lineages, such as the leukocyte-specific
α
and 8
β
2
inte-
grins. The integrin receptor has a large extracellular domain formed by both
α
β
subunits, a single transmembrane pass, and two short cytoplasmic
tails that do not contain catalytic motifs. The extracellular portions of the re-
ceptor also contain divalent metal-ion-binding sites, which are required for
functional binding. Most integrins recognize short peptide sequences, such
as the arginine-glycine-aspartic acid (RGD) motif present in many ECM pro-
and
β
Table 1
Selected integrins and their ligands
Integrin
Ligand
Binding site
α
1
β
1
COL-IV
CNBr frag. a1(IV)2
LN
E1-4, P1
α
2
β
1
COL-I
GFOGER (triple helix)
α
3
β
1
LN
E3, GD6 peptide
Thrombospondin
TSP-768
α
4
β
1
FN
IIICS (EILDV, REDV)
Osteopontin
Hep II (IDAPS)
α
5
β
1
FN
RGD + PHRSN
α
6
β
1
LN
E8
α
IIb
β
3
Fibrinogen
RGD (a); KQAGD (g)
FN
RGD
Vitronectin
RGD
von Willebrand factor
RGD
α
V
β
3
FN
RGD
Vitronectin
RGD
Fibrinogen
RGD
von Willebrand factor
RGD
Thrombospondin
RGD
Osteopontin
RGD
Bone sialoprotein
RGD
Te n a s c i n
RG D
COL (nonfibrillar)
RGD
α
M
β
2
Fibrinogen
P1, P2
iC3b
Factor X
