Molecular map of the desmosomal plaque

Abstract

Recent biochemical and molecular approaches have begun to establish the protein interactions that lead to desmosome assembly. To determine whether these associations occur in native desmosomes we have performed ultrastructural localisation of specific domains of the major desmosomal components and have used the results to construct a molecular map of the desmosomal plaque. Antibodies directed against the amino- and carboxy-terminal domains of desmoplakin, plakoglobin and plakophilin 1, and against the carboxy-terminal domains of desmoglein 3, desmocollin 2a and desmocollin 2b, were used for immunogold labelling of ultrathin cryosections of bovine nasal epidermis. For each antibody, the mean distance of the gold particles, and thus the detected epitope, from the cytoplasmic surface of the plasma membrane was determined quantitatively. Results showed that: (i) plakophilin, although previously shown to bind intermediate filaments in vitro, is localised extremely close to the plasma membrane, rather than in the region where intermediate filaments are seen to insert into the desmosomal plaque; (ii) while the ‘a’ form of desmocollin overlaps with plakoglobin and desmoplakin, the shorter ‘b’ form may be spatially separated from them; (iii) desmoglein 3 extends across the entire outer plaque, beyond both desmocollins; (iv) the amino terminus of desmoplakin lies within the outer dense plaque and the carboxy terminus some 40 nm distant in the zone of intermediate filament attachment. This is consistent with a parallel arrangement of desmoplakin in dimers or higher order aggregates and with the predicted length of desmoplakin II, indicating that desmoplakin I may be folded or coiled. Thus several predictions from previous work were borne out by this study, but in other cases our observations yielded unexpected results. These results have significant implications relating to molecular interactions in desmosomes and emphasise the importance of applying multiple and complementary approaches to biological investigations.

Dsg1 and Dsg3 Composition of Desmosomes Across Human Epidermis and Alterations in Pemphigus Vulgaris Patient Skin

“…Figure 1 depicts a representation of a desmosomal sub-unit, showing the localization of each protein as described in the literature, sizes and distances depicted are mostly based on the work of North et al. ( 20 ). To sensitively detect co-localization of the proteins, antibodies against epitopes in close proximity within the desmosomal intracellular region were selected ( Figure 1A ).…”

Architecture and dynamics of a novel desmosome-endoplasmic reticulum organelle

“…S2). The cytoplasmic zone of the desmosome comprises an electron-dense outer plaque adjacent to the plasma membrane and a less electron-dense inner plaque that functions as an attachment zone for keratin intermediate filaments ( 10, 11 ). FIB-SEM imaging and 3D reconstructions revealed that peripheral ER tubules were in close contact with desmosomal plaques (Fig.…”

“…The keratin intermediate filament cytoskeleton anchors to the desmosome inner dense plaque, leading to the formation of a symmetrical adhesion structure ( 11 ). Since peripheral ER tubules were observed on either side of the desmosome, we investigated ER tubule localization relative to keratin filament bundles proximal and distal to desmosomal cell contacts.…”

Mechanisms Causing Acantholysis in Pemphigus-Lessons from Human Skin

“…Desmosomes are recognized in electron micrographs by spatial distribution of electron dense plaques of varying densities identified as outer dense plaques (ODP), inner dense plaques (IDP), and extracellular core (EC) (23,24) (Figure 1A). The components of these plaques were identified using immunoelectron microscopy (25).…”

“…The components of these plaques were identified using immunoelectron microscopy (25). A more precise localization of the terminal domains of the main desmosomal proteins has been achieved using the quantitative immunogold method (23). Accordingly, the intracellular core of Dsg and Dsc, Pg and Pkp, as well as the N terminus of Dp constitute the ODP, whereas the N domain of Dp forms the IDP (23) and anchors the desmosomal plaques to the intermediate filament cytoskeleton (26).…”