FACIT collagen

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FACIT collagen stands for fibril-associated collagens with interrupted triple helices. They are a special type of collagen and proteoglycan that attach to collagen fibrils and share features with other extracellular matrix (ECM) molecules. Unlike the long, rope-like fibrillar collagens, FACITs have breaks in their triple-helical structure, which adds flexibility and creates extra binding sites for other ECM components.

FACITs help assemble and organize collagen fibrils and other ECM parts, and they modify the surface properties of fibrils to shape tissue-specific ECM patterns. Their structure includes short triple-helical segments interrupted by non-helical regions, with parts facing the space between fibers.

There are eight known FACIT types: collagens IX, XII, XIV, XVI, XIX, XXI, and XXII (the COL22A1 gene encodes collagen XXII). They are found in many tissues, including cartilage (IX, XIV), tendons and ligaments (XII, XIV), skin, and other areas. Some FACITs interact with enzymes that modify fibrils and provide binding sites for other matrix molecules. They can also be present in basement membranes and at myotendinous junctions, as well as in tissues like the cornea and certain brain regions.

In short, FACIT collagens help shape and stabilize collagen networks, giving tissues strength and the right level of flexibility.