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Examining Skin: A Functional Barrier

By: Marie Alice Dibon, PharmD
Posted: March 2, 2012, from the March 2012 issue of GCI Magazine.

page 4 of 13

It is important here, before examining structural proteins, to note the “active” proteins that these enzymes constitute.

Enzymes intervene in a number of metabolisms, allowing structural proteins to link up (transglutaminases I) to form a stronger barrier as well as break these bonds (proteolytic enzymes). They also allow desquamation. But there are also antioxidant enzymes (SOD) protecting the proteins from oxidation, or histidase, allowing for the production of urocanic acid, the skin’s own sun protectant.

Structural Proteins: Building a Strong Yet Flexible Barrier

Structural proteins are the main component of the horny layers, the outermost layer of the skin. Keratin and its various forms are the most common.

During the differentiation process, the cornified envelope replaces the plasma membrane of differentiating keratinocytes. It consists of keratins that are enclosed within an insoluble amalgam of proteins, which are crosslinked by transglutaminases and surrounded by a lipid envelope.

But there are other proteins forming the structure of the stratum corneum—such as filagrin and involucrin. These are very important players in the structure of the skin barrier function, and their role is to link the lipids with the key elements of the corneocytes structure, the cornified envelope, through covalent liaisons. The term “covalent” means that those liaisons are strong and hard to break, allowing for the lipids to stick to the cells and for the skin to maintain the essential lipidic mantle produced during the differentiation process.

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