Nidogen/nidogen/Entactin/entactin/nidogen-1/Nidogen-1
The nidogen family, representing multivalent matrix binding proteins, consists in mammals of two members, nidogen-1 and -2. They are considered as classical linkers joining laminin and collagen IV networks in basement membranes. Lack of both nidogens completely prevented BM deposition and ultrastructural assembly of BM and hemidesmosomes, although other BM proteins remained detectable at comparable levels with no signs of degradation. Supplementation by recombinant nidogen-1 or -2 restored these structures.
Nidogen-1 also named Entactin is an integral and ubiquitous component of the basement membrane. In human, it is encoded by the NID1 gene. The amino acid sequences of the mouse and human molecules have been determined and exhibit 85% sequence identity. The molecule is organized into three structural domains, an N-terminal globule (I) is linked to a smaller C-terminal globule (III) by a rigid stalk (II) largely consisting of cysteine-rich EGF-like homology repeats and a cysteine-rich thyroglobulin homology repeat.
Nidogen-1 binds calcium ions and this calcium-binding activity of entactin may play a role in the matrix assembly process. Its major function appear to be the assembly of the basement membrane. The carboxyl globule binds tightly to one of the short arms of laminin at the inner rodlike segment. This same region is also believed to be responsible for the attachment of nidogen-1 to type IV collagen at approximately 80 nm from its carboxyl noncollagenous end. Nidogen-1 therefore could serve as a bridge between the two most abundant molecules in the basement membrane.
The protease sensitivity of nidogen-1 suggests that it may be a target for proteolytic activity during tissue remodeling, metastasis, and other events requiring the turnover of the basement membrane.
Entactin/Nidogen-1 supports also cell adhesion.
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