Characterization of precrystallization aggregation of canavalin by dynamic light scattering.

The aggregation processes leading to crystallization and precipitation of canavalin have been investigated by dynamic light scattering (DLS) in photon correlation spectroscopy (PCS) mode. The sizes of aggregates formed under various conditions of pH, salt concentration, and protein concentrations were deduced from the correlation functions generated by the fluctuating intensity of light scattered by the solutions of the protein. Results obtained indicate that the barrier to crystallization of canavalin is the formation of the trimer, a species that has been characterized by x-ray crystallographic studies (McPherson, A. 1980. J. Biol. Chem. 255:10472-10480). The dimensions of the trimer in solution are in good agreement with those obtained both from the crystal (McPherson, A. 1980. J. Biol. Chem. 255:10472-10480) and from a low angle x-ray scattering study in solution (Plietz, P., P. Damaschun, J. J. Müller, and B. Schlener. 1983. FEBS [Fed. Eur. Biochem. Soc.] Lett. 162:43-46). Furthermore, under conditions known to lead to the formation of rhombohedral crystals of canavalin, a limiting size is reached at high concentrations of canavalin. The size measured corresponds to an aggregate of trimers making a unit rhombohedral cell consistent with x-ray crystallographic data (McPherson, A. 1980. J. Biol. Chem. 255:10472-10480). Presumably, such aggregates are the nuclei from which crystal growth proceeds. The present study was undertaken primarily to test the potential of DLS (PCS) as a tool for rapid, routine screening to determine the ultimate fate of protein solutions (i.e., crystallization or amorphous precipitation) at an early stage, therefore eliminating the need for long-term visual observation. Achieving this goal would constitute amajor advance in the practive of protein crystallization. Delays imposed by visual observation would be considerably reduced, and a more systematic approach could be adopted to select experimental conditions.Our findings with canavalin demonstrate that DLS(PCS) is, indeed, a selective and sensitive probe of precrystallization conditions. Other advantages of this technique include the facts that it is noninvasive, nondestructive,universal, and does not require calibration

Functional implications of structure-based sequence alignment of proteins in the extracellular pectate lyase superfamily.

International audienc

Investigation of folding of purified recombinant GRA1 protein using w3eb based protein disorder servers and trypsin digestion

PubMed ID: 19601915The successful folding of a recombinant protein after expression and purification is essential for structural, biochemical and vaccination studies. Toxoplasma gondii recombinant GRA1 protein is a promising vaccine candidate against toxoplasmosis. In the present study, the folding of recombinant GRA1 protein has been evaluated by web based bioinformatics tools that predict protein folding. Subsequently, trypsin digestion, which is a simple indication of proper protein folding, has been used to determine whether recombinant GRA1 protein is likely to be folded. The results indicate that the recombinant GRA1 protein is predicted to be folded by most of the web based bioinformatics predictors. Moreover, in protease digestion experiments, the recombinant GRA1, which was purified to homogeneity without the use of denaturants, gives rise to a discrete band pattern that is indicative of a folded protein. Together, the results suggest that recombinant GRA1 protein is in a folded conformation, suitable for structu al, biochemical and vaccination studies. © 2009 Bentham Science Publishers Ltd

Structure-based multiple alignment of extracellular pectate lyase sequences

International audienc

The structure of a DNA unwinding protein and its complexes with oligodeoxynucleotides by x-ray diffraction.

The structure of the gene 5 DNA unwinding protein from bacteriophage fd has been solved to 2.3 A resolution by x-ray diffraction techniques. The molecule contains an extensive cleft region that we have identified as the DNA binding site on the basis of the residues that comprise its surface. The interior of the groove has a rather large number of basic amino acid residues that serve to draw the polynucleotide backbone into the cleft. Arrayed along the external edges of the groove are a number of aromatic amino acid side groups that are in position to stack upon the bases of the DNA and fix it in place. The cleft then acts as an elongated pair of jaws that draws the DNA between them by charge interactions involving the phosphates with the interior lysines and arginines. The jaws then close on the DNA strand through small conformation changes and the rotation of aromatic side-chains into position to stack upon the purines and pyrimidines. Complexes of the gene 5 protein with a variety of oligodeoxynucleotides have been formed and crystallized for x-ray diffraction analysis. The crystallographic parameters of four different unit cells indicate that the fundamental unit of the complex is composed of six gene 5 protein dimers. We believe this aggregate has 622 point group symmetry and is a ring formed by end to end closure of a linear array of six dimers. From our results we have proposed a double helical model for the gene 5 protein-DNA complex in which the protein forms a spindle or core around which the DNA is spooled. 5.0-A x-ray diffraction data from one of the crystalline complexes is currently being analyzed by molecular replacement techniques to obtain what we believe will be the first direct visualization of a protein-deoxyribonucleic acid complex approaching atomic resolution