No abstract

Crystals of tetragonal hen egg-white lysozyme were grown using Advanced Protein Crystallization Facility (APCF) apparatus under a microgravity environment (SpaceHab-01 mission) and ground control conditions. Crystals were grown from NaCI as a crystallizing agent at pH 4.3. The X-ray diffraction patterns of the best diffracting ground-and space-grown crystals were recorded using synchrotron radiation and an image plate on the W32 beamline at LURE. Both ground-and space-grown crystals showed nearly equivalent maximum resolution of 1.3-1.4,~. Refinements were carried out with the program X-PLOR with final R values of 18.45 and 18.27% for structures from ground-and spacegrown crystals, respectively. The two structures are nearly identical with the root-mean-square difference on all protein atoms being 0.13/~. Some residues of the two refined structures show multiple alternative conformations. Two ions were localized into the electron-density maps of the two structures: one chloride ion at the interface between two symmetry-related molecules and one sodium ion stabilizing the loop Ser60-Leu75. The sodium ion is surrounded by six ligands which form a bipyramid around it at distances of 2.2-2.6 A,.

The mammalian growth factor receptor-binding protein Grb2 is an adaptor that mediates activation of guanine nucleotide exchange on Ras. Grb2 binds to the receptor through its SH2 domain and to the carboxyl-terminal domain of Son of sevenless through its two SH3 domains. It is thus a key element in the signal transduction pathway. The crystal structure of Grb2 was determined to 3.1 angstrom resolution. The asymmetric unit is composed of an embedded dimer. The interlaced junctions between the SH2 and SH3 domains bring the two adjacent faces of the SH3 domains in van der Waals contact but leave room for the binding of proline-rich peptides.

Involved in the coagulation cascade, factor Xa (FXa) is a serine protease which has received great interest as a potential target for the development of new antithrombotics. Although there is a great wealth of structural data on thrombin complexes, few structures of ligand/FXa complexes have been reported, presumably because of the difficulty in growing crystals. Reproducible crystallization conditions for human des-Gla1-45 coagulation FXa have been found. This has led to an improvement in the diffraction quality of the crystals (about 2.1 A) when compared to the previously reported forms (2.3-2.8 A) thus providing a suitable platform for a structure-based drug design approach. A series of crystal structures of noncovalent inhibitors complexed with FXa have been determined, three of which are presented herein. These include compounds containing the benzamidine moiety and surrogates of the basic group. The benzamidine-containing compound binds in a canonical fashion typical of synthetic serine protease inhibitors. On the contrary, molecules that contain surrogates of the benzamidine group do not make direct hydrogen-bonding interactions with the carboxylate of Asp189 at the bottom of the S1 pocket. The structural data provide a likely explanation for the specificity of these inhibitors and a great aid in the design of bioavailable potent FXa inhibitors.