Solution structure and dynamics of a prototypical chordin-like cysteine-rich repeat (von Willebrand factor type C module) from collagen IIA

Chordin-like cysteine-rich (CR) repeats (also referred to as von Willebrand factor type C (VWC) modules) have been identified in ∼200 extracellular matrix proteins. These repeats, named on the basis of amino acid conservation of 10 cysteine residues, have been shown to bind members of the transforming growth factor-β (TGF-β) superfamily and are proposed to regulate growth factor signaling. Here we describe the intramolecular disulfide bonding, solution structure, and dynamics of a prototypical chordin-like CR repeat from procollagen IIA (CR_ColIIA), which has been previously shown to bind TGF-β1 and bone morphogenetic protein-2. The CR_ColIIA structure manifests a two sub-domain architecture tethered by a flexible linkage. Initial structures were calculated using RosettaNMR, a de nova prediction method, and final structure calculations were performed using CANDID within CYANA. The N-terminal region contains mainly β-sheet and the C-terminal region is more irregular with the fold constrained by disulfide bonds. Mobility between the N- and C-terminal sub-domains on a fast time-scale was confirmed using NMR relaxation measurements. We speculate that the mobility between the two sub-domains may decrease upon ligand binding. Structure and sequence comparisons have revealed an evolutionary relationship between the N-terminal sub-domain of the CR module and the fibronectin type 1 domain, suggesting that these domains share a common ancestry. Based on the previously reported mapping of fibronectin binding sites for vascular endothelial growth factor to regions containing fibronectin type 1 domains, we discuss the possibility that this structural homology might also have functional relevance.