DESMOSOME
The desmosome provides the major connection between one keratinocyte and another. It is the most complex of the keratinocyte connection points, which also include tight junctions, adherens junctions, and gap junctions. Desmosomes are present on all keratinocytes from the stratum basalis through the stratum granulosum. Once they reach the stratum corneum, the desmosomes start to degrade and break apart as the corneocytes are desquamated off the surface of the skin. The main purpose of desmosomes is to connect the actin cytoskeleton of one keratinocyte to that of the adjacent keratinocyte. They achieve this goal through a series of highly coordinated protein connections. The main proteins that allow for the connection between adjacent cells and the strength of the connection are the cadherin proteins, desmoglein and desmocollin. These are calcium-dependent adhesion molecules. Desmoglein and desmocollin are transmembrane proteins. A desmocollin protein from one keratinocyte interacts with a desmoglein protein from the adjacent keratinocyte in a one-to-one ratio. There is more than one type of desmogleins and desmocollins, but they all interact similarly. Some of the subtypes are expressed at slightly different rates in various locations such as mucous membranes and the different levels of the epidermis. Each desmoglein or desmocollin molecule is anchored within the keratinocyte to plakoglobin, which in turn is bound to a group of proteins named desmoplakins. The desmoplakin proteins ultimately connect with the intercellular actin cytoskeleton.
The pemphigus group of diseases are autoimmune blistering diseases caused by the formation of autoantibodies against desmoglein and, in some cases, also against desmocollin. These autoantibodies interrupt the cell-to-cell adhesion process, resulting in superficial blistering of the skin and mucous membranes.
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