• SP1;
  • stress-responsive proteins;
  • chaperone-like proteins.

SP1 (108 amino acids) is a boiling-stable stress-responsive protein. It has no significant sequence homology to other stress-related proteins or to small heat-shock proteins (sHsps). SP1 activity is ATP-independent, similar to other small heat-shock proteins. Based on these features, it is expected that the structure–function relationship of SP1 will be unique. In this work, the crystallization and preliminary crystallographic data of native SP1 and its selenomethionine derivative are described. Recombinant SP1 and its selenomethionine derivative were expressed in Escherichia coli and used for crystallization experiments. SP1 crystals were grown from 0.1 M HEPES pH 7.5, 20% PEG 3K, 0.2 M NaCl. One to four single crystals appeared in each droplet within a few days and grew to dimensions of about 0.5 × 0.5 × 0.8 mm after about two weeks. Diffraction studies of these crystals at low temperature indicated that they belong to space group I422, with unit-cell parameters a = 89, b = 89, c = 187 Å. Efforts to crystallize the selenomethionine derivative of SP1 are in progress.