Revisiting the mystery of fibronectin multimers: The fibronectin matrix is composed of fibronectin dimers cross-linked by non-covalent bonds

Fibronectin (FN) matrix fibrils have long been thought to be formed by disulfide-bonded FN multimers, although there is no direct evidence that they are covalently linked with each other. To understand the biochemical properties of these fibrils, we extracted a crude FN matrix from FN-YPet transfected 3T3 cell culture using 0.2% deoxycholate and DNase. The insoluble extracted matrix preserved fibrillar structures and a major portion of the extracted proteins migrated as FN monomers on an SDS gel under reducing conditions. Under non-reducing conditions, some FN molecules appeared to be trapped at the top of the stacking gel. We tested this by mixing fluorescently labeled FN dimers with the extracted matrix just before loading on an SDS gel, and found that mo