1H NMR assignment and secondary structure of the cell adhesion type III module of fibronectin.

The secondary structure of the tenth type III module from human fibronectin has been determined using NMR. This type of module appears many times in a wide variety of proteins. The type III module described here contains an Arg-Gly-Asp sequence known to be involved in cell-cell adhesion. The module was expressed in yeast and characterized by amino acid sequencing and mass spectrometry. 2D and 3D NMR spectroscopy of 15N-labeled protein was used to perform sequence-specific assignment of the spectrum. The secondary structure was defined by patterns of nuclear Overhauser effects, 3JNH-alpha CH spin-spin coupling constants, and amide proton solvent exchange rates. The molecule consists of seven beta-strands in two antiparallel beta-sheets with an immunoglobulin-like fold similar to that predicted for homologous modules in the cytokine receptor super family [Bazan, J. F. (1990) Proc. Natl. Acad. Sci. U.S.A. 87, 6934-6938]. The Arg-Gly-Asp sequence is located on a loop between the beta-strands F and G.