Molecular Biology of the Cell by Bruce Alberts, Alexander Johnson, Julian Lewis, David Morgan, Martin Raff, Keith Roberts, Peter Walter by by Bruce Alberts, Alexander Johnson, Julian Lewis, David Morg

1046 Chapter 19: Cell Junctions and the Extracellular Matrix
nonclassical
cadherin proteins
desmoplakin
plakoglobin
plakophilin
adaptor proteins
intermediate
filaments
dense plaque of
adaptor proteins
desmoglein
desmocollin
nonclassical
cadherin
proteins
(B)
intermediate
filaments
plasma membrane
CYTOSOL
CYTOSOL
(A)
plasma
membranes
(C)
(D)
0.5 µm 100 nm
Figure 19–16 Desmosomes. (A) The structural components of a desmosome. On the cytoplasmic surface of each interacting
plasma membrane is a dense plaque composed of a mixture of intracellular adaptor proteins. A bundle of keratin intermediate
filaments is attached to the surface of each plaque. Transmembrane nonclassical cadherins bind to the plaques and interact
through their extracellular domains to hold the adjacent membranes together. (B) Some of the molecular components of a
desmosome. Desmoglein and desmocollin are nonclassical cadherins. Their cytoplasmic tails bind plakoglobin (γ-catenin)
and plakophilin (a distant relative of p120-catenin), which in turn bind to desmoplakin. Desmoplakin binds to the sides of
intermediate filaments, thereby tying the desmosome to these filaments. (C) An electron micrograph of desmosome junctions
between three epidermal cells in the skin of a baby mouse. (D) Part of the same tissue at higher magnification, showing a single
desmosome, with intermediate filaments attached to it. (C and D, from W. He, P. Cowin and D.L. Stokes, Science 302:109–113,
2003. With permission from AAAS.)
MBoC6 m19.17/19.16
in vertebrates but are not found, for example, in Drosophila. They are present in
most mature vertebrate epithelia and are particularly plentiful in tissues that are
subject to high levels of mechanical stress, such as heart muscle and the epidermis,
the epithelium that forms the outer layer of the skin.
Figure 19–16A shows the general structure of a desmosome, and Figure
19–16B shows some of the proteins that form it. Desmosomes typically appear as
buttonlike spots of adhesion, riveting the cells together (Figure 19–16C). Inside
the cell, the bundles of ropelike intermediate filaments that are anchored to
the desmosomes form a structural framework of great tensile strength (Figure
19–16D), with linkage to similar bundles in adjacent cells, creating a network that
extends throughout the tissue (Figure 19–17). The particular type of intermediate
filaments attached to the desmosomes depends on the cell type: they are keratin
filaments in most epithelial cells, for example, and desmin filaments in heart
muscle cells.
The importance of desmosomes is demonstrated by some forms of the potentially
fatal skin disease pemphigus. Affected individuals make antibodies against
one of their own desmosomal cadherin proteins. These antibodies bind to and
disrupt the desmosomes that hold their epidermal cells (keratinocytes) together.
This results in a severe blistering of the skin, with leakage of body fluids into the
loosened epithelium.