The relative orientation of the fibronectin 6F11F2 module pair: A 15N NMR relaxation study

The structure of a pair of modules (⁶F1¹F2), that forms part of the collagen-binding region of fibronectin, is refined using heteronuclear relaxation data. A structure of the pair was previously derived from ¹H-¹H NOE and (³J)H(α) HN data [Bocquier et al. (1999) Structure, 7, 1451-1460] and a weak module-module interface, comprising Leu19 and Leu28, in ⁶F1, and Tyr68 in ²F1, was identified. In this study, the definition of the average relative orientation of the two modules is improved using the dependence of ¹⁵N relaxation on rotational diffusion anisotropy. This structure refinement is based on the selection of a subset of structures from sets calculated with NOE and (³J)H(α) HN data alone, using the quality of the fits to the relaxation data as the selection criterion. This simple approach is compared to a refinement strategy where ¹⁵N relaxation data are included in the force field as additional restraints.