Cell Junctions, Structure, Function, and Regulation
349
CAR site
3 Ca
++
A
EC1 domain
Trp-2
Juxtamembrane domain
Catenin binding domain
Fig. 10
Cadherin monomer. Schematic showing
the important sites that are implicated in the
regulation of cadherin-mediated adhesion,
including the Frst cadherin repeat (EC1 domain),
the N-terminal tryptophan (Trp2), cell adhesion
recognition site (CAR site), calcium (Ca
++
)
binding sites, the juxtamembrane region, and
catenin binding domain.
Trp2 residue in the type II cadherins
desmocollin and desmoglein, one also
fnds a high degree oF sequence similarity
within each type or Family oF cadherin. In
addition to sequence similarities, genomic
organization is also used to classiFy cad-
herins. ±or example, the precursor region
and the cytoplasmic tail oF atypical/type II
cadherins are encoded by a single exon,
whereas these regions in other cadherins
contain one or more introns. The type II
cadherins also contain two extra introns
in the sequence coding the extracellular
region that is not Found in other cadherin
Families. On the basis oF these structural
and genomic similarities members oF the
cadherin Family have been divided into
Families as shown in Table 6.
2.3
Type I/II Cadherins and Adherens Junctions
The binding oF cadherins and the Forma-
tion oF stable AJs is a multistep process.
The Formation oF cell–cell junctions by
classical cadherins has been extensively
studied in epithelial cells. In epithelial
cells, cadherins are diFFusely spread on
the cell surFace prior to cell–cell contact.
Cells frst approach one another through
the Formation oF flopodia. As the flopodia
From adjacent cells come into contact, cad-
herins Form small clusters at the flopodia
tip and recruit the proteins that promote
cortical actin assembly. These clusters are
brought into larger plaque-like structures
as the cortical actin remodels. The binding
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