Abstract
α-Helical coiled coils, frequent protein oligomerization motifs, are commonly observed in vital proteins. Here, using collagen XVII as an example, we provide evidence for a novel function of coiled coils in the regulation of ectodomain shedding. Transmembrane collagen XVII, an epithelial cell surface receptor, mediates dermal-epidermal adhesion in the skin, and its dysfunction is linked to human skin blistering diseases. The ectodomain of this collagen is constitutively shed from the cell surface by proteinases of a disintegrin and metalloprotease family; however, the mechanisms regulating shedding remain elusive. Here, we used site-specific mutagenesis to target the coiled-coil heptad repeats within the juxtamembranous, extracellular noncollagenous 16th A (NC16A) domain of collagen XVII. This resulted in a substantial increase of ectodomain shedding, which was not mediated by disintegrin and metalloproteases. Instead, conformational changes induced by the mutation(s) unmasked a furin recognition sequence that was used for cleavage. This study shows that apart from their functions in protein oligomerization, coiled coils can also act as regulators of ectodomain shedding depending on the biological context.
Highlights
␣-Helical coiled coils, frequent protein oligomerization motifs, are commonly observed in vital proteins
The amino acid sequence of this region in collagen XVII is highly conserved among different species (Fig. 1A), suggesting that it has a vital function
Full-length collagen XVII is a homotrimer of three 180-kDa polypeptides, and the shedding generates an ectodomain consisting of three 120
Summary
We used site-specific mutagenesis to target the coiled-coil heptad repeats within the juxtamembranous, extracellular noncollagenous 16th A (NC16A) domain of collagen XVII This resulted in a substantial increase of ectodomain shedding, which was not mediated by disintegrin and metalloproteases. The first cue of functional association of coiled coils and ectodomain shedding in transmembrane collagens comes from the fact that the coiled-coil heptad repeats are located within the juxtamembranous noncollagenous domains adjacent to the cell surface, which harbor the sheddase recognition and cleavage sites [8, 9, 24]. We targeted the coiled-coil heptad repeats in the NC16A domain using site-directed mutagenesis and uncovered a novel and essential role of the coiled coils within the NC16A domain in the regulation of collagen XVII ectodomain shedding
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