The relative orientation of the fibronectin 6F1(1)F2 module pair: a 15N NMR relaxation study.

The structure of a pair of modules (6F1(1)F2), 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(HalphaHN) 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(HalphaHN) 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 [Tjandra et al. (1997) Nat. Struct. Biol., 4, 443-449].