Facilities and methods for the high-throughput crystal structure analysis of human proteins are described as recently established in the Protein Structure Factory, a Berlin-area structural genomics project. Genes encoding human proteins are expressed in either recombinant Escherichia coli or yeast (Saccharomyces cerevisiae or Pichia pastoris). To facilitate and standardize protein purification, the target proteins are produced with various tags for affinity chromatography. For high-throughput crystallization, a robotic station is being set up that has the capacity to handle 960 000 experiments simultaneously. The resulting protein crystals will be subjected to X-ray diffraction experiments at the third-generation synchrotron storage ring BESSY where protein crystallography beamlines are currently under construction. The Protein Structure Factory's strategy for high-throughput production and structure analysis of human proteins is evaluated based on first results.

Static and dynamic light scattering have been employed to investigate the behaviour of lysozyme solutions when varying the concentration of (NH4)2SO 4 and NaC1 for screening the repulsive forces between the monomers. At the initial aggregation stages clusters, which can be classified as mass-fractals undergoing diffusion limitedlike aggregation, coexist with monomers or small lysozyme oligomers. The kinetics of fractal growth deliver observables that exhibit distinct tendencies when examined as a function of the concentration and nature of the electrolyte. The behaviour of the observables changes drastically above 0.84M (NH4)2SO 4 and 0.60M NaCl. Static light scattering revealed a progressive restructuring of the fractals to compact structures at the latter stages of the reaction. Based on the correlations between the various observables an attempt is made to predict the long-term fate of the nucleating solutions.

Helicases are ATP-driven enzymes essential for DNA unwinding. The broad host range plasmid RSFI010 harbours a gene (repA) encoding for one of the smallest known oligomeric helicases, RepA, a homo-hexamer with 30 kDa subunits. Electron micrographs indicate that the overall shape of RepA resembles a hexagon with globular monomers at the corners, diameter 140 A, and a central channel. Below pH 6, the molecules aggregate into tubular structures. The enzyme has been purified and crystallized using the hanging-drop vapour-diffusion method with polyethyleneglycol monomethylether as precipitating agent. The crystals exhibit the monoclinic space group P2(1) with unit-cell parameters a = 105.8, b = 180.3, c = 115.4 A, beta = 95.2 degrees, and diffract to 3.5 A resolution using rotating-anode Cu Kalpha radiation. Assuming two 180 kDa molecules per asymmetric unit, the volume per unit weight is V(m) = 3.06 A Da(-1), equivalent to a solvent content of 60%. A self-rotation search indicates that the sixfold axis of the hexamer is parallel to the ac plane and inclined at about 2 degrees to the c axis. The two hexamers are oriented head-to-head with point-group symmetry D(6).

The cluster formation in nucleating hen egg white lysozyme−NaCl solutions was studied by simultaneous static and dynamic light scattering. Angular dependence measurements of the total scattered intensity and of the average cluster diffusion coefficient revealed the appearance of pronounced structure factor peaks at the initial nucleation stages. Such peaks are characteristic for the ordering often observed in highly concentrated colloidal suspensions. Free-energy minimizations of 4−60 particles, that adequately model the lysozyme monomer, were performed by using the effective interaction potentials described in previous work (Soumpasis; Georgalis Biophys. J. 1997, 72, 2770). Both experiment and computations show formation of clusters with fractal morphology, compatible with the findings of the present and previous works.