Abstract
Collagens are a group of extracellular matrix proteins with essential functions for skin integrity. Anchoring fibrils are made of type VII collagen (Col7) and link different skin layers together: the basal lamina and the underlying connective tissue. Col7 has a central collagenous domain and two noncollagenous domains located at the N and C terminus (NC1 and NC2), respectively. A cysteine-rich region of hitherto unknown function is located at the transition of the NC1 domain to the collagenous domain. A synthetic model peptide of this region was investigated by CD and NMR spectroscopy. The peptide folds into a collagen triple helix, and the cysteine residues form disulfide bridges between the different strands. The eight cystine knot topologies that are characterized by exclusively intermolecular disulfide bridges have been analyzed by molecular modeling. Two cystine knots are energetically preferred; however, all eight disulfide bridge arrangements are essentially possible. This novel cystine knot is present in type IX collagen, too. The conserved motif of the cystine knot is CX3CP. The cystine knot is N-terminal to the collagen triple helix in both collagens and therefore probably impedes unfolding of the collagen triple helix from the N terminus.
Highlights
Type VII collagen is essential for skin stability as highlighted by related skin blistering diseases
Col7 is the major component of anchoring fibrils that are found at the dermal epidermal junction
A cysteine-rich region with unknown function is located at the transition of the N-terminal NC1 domain and the central collagen triple helix
Summary
Type VII collagen is essential for skin stability as highlighted by related skin blistering diseases. Conclusion: The cysteine-rich region is an N-terminal cystine knot with novel topology. Anchoring fibrils are made of type VII collagen (Col7) and link different skin layers together: the basal lamina and the underlying connective tissue. A cysteine-rich region of hitherto unknown function is located at the transition of the NC1 domain to the collagenous domain. The peptide folds into a collagen triple helix, and the cysteine residues form disulfide bridges between the different strands. The eight cystine knot topologies that are characterized by exclusively intermolecular disulfide bridges have been analyzed by molecular modeling. Two cystine knots are energetically preferred; all eight disulfide bridge arrangements are essentially possible. This novel cystine knot is present in type IX collagen, too. The cystine knot is N-terminal to the collagen triple helix in both collagens and probably impedes unfolding of the collagen triple helix from the N terminus
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