Structure of the hypothetical protein TTHA1873 from Thermus thermophilus.

The crystal structure of an uncharacterized hypothetical protein, TTHA1873 from Thermus thermophilus, has been determined by X-ray crystallography to a resolution of 1.78 Å using the single-wavelength anomalous dispersion method. The protein crystallized as a dimer in two space groups: P4 3 2 1 2 and P6 1 22. Structural analysis of the hypothetical protein revealed that the overall fold of TTHA1873 has a β-sandwich jelly-roll topology with nine β-strands. TTHA1873 is a dimeric metal-binding protein that binds to two Ca 2+ ions per chain, with one on the surface and the other stabilizing the dimeric interface of the two chains. A structural homology search indicates that the protein has moderate structural similarity to one domain of cell-surface proteins or agglutinin receptor proteins. Red blood cells showed visible agglutination at high concentrations of the hypothetical protein.