SOLUTION STRUCTURE OF THE ACTIVE DOMAIN OF TISSUE INHIBITOR OF METALLOPROTEINASES .2. A NEW MEMBER OF THE OB FOLD PROTEIN FAMILY

Homonuclear two-dimensional and three-dimensional H-1 nuclear magnetic resonance spectroscopy has been used to obtain essentially complete sequence-specific assignments for 123 of the 127 amino acid residues present in the truncated form of tissue inhibitor of metalloproteinases-2 (Delta TIMP-2), the active N-terminal domain of the protein. Analysis of the through-space nuclear Overhauser effect data obtained for Delta TIMP-2 allowed determination of both the secondary structure of the domain and also a low-resolution tertiary structure defining the protein backbone topology. The protein contains a five-stranded antiparallel beta-sheet that is rolled over on itself to form a closed beta-barrel, and two short helices which pack close to one another on the same barrel face. A comparison of the Delta TIMP-2 structure with other known protein folds reveals that the beta-barrel topology is homologous to that seen in proteins of the oligosaccharide/oligonucleotide binding (OB) fold family. The common structural features include the number of beta-strands and their arrangement, the beta-barrel shear number, an interstrand hydrogen bond network, the packing of the hydrophobic core, and a conserved beta-bulge. Superpositions of the beta-barrels from Delta TIMP-2 and two previously known members of the OB protein fold family (staphylococcal nuclease and Escherichia coli heat-labile enterotoxin) confirmed the similarity in beta-barrel topology. The three-dimensional structure of Delta TIMP-2 has allowed a more detailed interpretation than was previously possible of the functional significance of available protein sequence and site-directed mutagenesis data for the TIMP family. Furthermore, the structure has revealed conserved surface regions of potential functional importance.