Yoshiho Nagata

Abstract Crystalline wheat germ agglutinin was prepared from unprocessed wheat germ by a new purification procedure. Its purity and some of its molecular characteristics were examined by a number of criteria. Sedimentation analysis gave a molecular weight of 17,000 ± 1,000 and a sedimentation coefficient of 2.1 S when determined in 0.05 n HCl. At neutral pH, the agglutinin dimerizes with a molecular weight of around 35,000 and a sedimentation coefficient of 3.6 S. Amino acid analyses indicate that the protein contains a high amount of glycine and half-cystine; none of the latter is present as cysteine. Three times crystallized agglutinin is devoid of neutral sugars. Equilibrium dialysis experiments using N-acetyl-[1-14C]glucosamine indicate that the agglutinin has 2-binding sites for N-acetylglucosamine per mole of the polypeptide chain with a dissociation constant of 7.6 x 10-4 m. This binding is highly specific. The β-1,4 di- and trisaccharides of N-acetylglucosamine showed higher affinities with apparent dissociation constants of 4.9 and 1.2 x 10-5 m, respectively.

Abstract Procedures for the isolation, purification, and crystallization of wheat germ agglutinin are described. The agglutinin was purified 184-fold to homogeneity from commercial wheat germ lipase. A molecular weight of 23,500 was estimated for the protein by means of sedimentation equilibrium and sodium dodecyl sulfate gel electrophoresis. The agglutinin is a glycoprotein. Amino acid and carbohydrate compositions are reported. The protein contains unusually high half-cystine and glycine. Glucose was found to be the major carbohydrate constituent.

Chitosanase from Bacillus circulans MH-K1 is a 29-kDa extracellular protein composed of 259 amino acids. The crystal structure of chitosanase from B. circulans MH-K1 has been determined by multiwavelength anomalous diffraction method and refined to crystallographic R = 19.2% (R(free) = 23.5%) for the diffraction data at 1.6-A resolution collected by synchrotron radiation. The enzyme has two globular upper and lower domains, which generate the active site cleft for the substrate binding. The overall molecular folding is similar to chitosanase from Streptomyces sp. N174, although there is only 20% identity at the amino acid sequence level between both chitosanases. However, there are three regions in which the topology is remarkably different. In addition, the disulfide bridge between Cys(50) and Cys(124) joins the beta1 strand and the alpha7 helix, which is not conserved among other chitosanases. The orientation of two backbone helices, which connect the two domains, is also different and is responsible for the differences in size and shape of the active site cleft in these two chitosanases. This structural difference in the active site cleft is the reason why the enzymes specifically recognize different substrates and catalyze different types of chitosan degradation.

Aleuria aurantia lectin (AAL) is a protein composed of two identical subunits having no carbohydrate chain and shows sugar-binding specificity for L-fucose. Full-length cDNA encoding for the lectin has been isolated from a lambda gt11 library, screened with an antiserum directed against AAL. The cDNA clone contained 1,370 nucleotides and an open reading frame of 939 nucleotides encoding 313 amino acids. The amino-terminal sequence (residues 1-30) of the lectin isolated from the mushroom coincided with the deduced amino acid sequence starting from proline at the 2nd residue, indicating that the mature AAL consists of 312 amino acids. Its molecular weight is calculated to be 33,398. The deduced amino acid sequence shows that AAL includes six internal homologous regions, and has considerable homology with a hemagglutinin from a Gram-negative bacterium, Myxococcus xanthus, which forms a fruiting body. No significant homology was observed with higher plant or animal lectins. The recombinant AAL produced by Escherichia coli JM109 carrying the AAL expression plasmid pKA-1 [Fukumori, F. et al. (1989) FEBS Lett. 250, 153-156] was purified from the cell lysate by affinity chromatography using a fucose-starch column, and hundreds of milligrams of the lectin was obtained. The recombinant lectin showed the same biochemical characteristics and sugar binding specificity as did the natural AAL.

A non-radioisotopic and sensitive method for quantification of specific DNA immobilized in microtiter wells has been developed. This method is based upon the immobilization of DNA in microtiter wells and hybridization with biotinylated DNA probe which is followed by complexing with avidin-beta-galactosidase. By measuring fluorescence emitted from the hydrolyzed product by beta-galactosidase of 4-methylumbelliferyl-beta-D-galactoside, it has become possible to quantify a few picograms of specific DNA in DNA samples immobilized in plastic microtiter wells.