Prolipoprotein signal peptidase of Escherichia coli requires a cysteine residue at the cleavage site

A signal peptidase specifically required for the secretion of the lipoprotein of the Escherichia coli outer membrane cleaves off the signal peptide at the bond between a glycine and a cysteine residue. This cysteine residue was altered to a glycine residue by guided site-specific mutagenesis using a synthetic oligonucleotide and a plasmid carrying an inducible lipoprotein gene. The induction of mutant lipoprotein production was lethal to the cells. A large amount of the prolipoprotein was accumulated in the outer membrane fraction. No protein of the size of the mature lipoprotein was detected. These results indicate that the prolipoprotein signal peptidase requires a glyceride modified cysteine residue at the cleavage site.     

Temperature-Sensitive Modification and Restriction Phenotypes of an Escherichia coli dnaD Mutant

A mutant of Escherichia coli temperature-sensitive for deoxyribonucleic acid synthesis, dnaD, was found to have temperature-sensitive modification and restriction phenotypes. In contrast to the original observation by Carl (1970), the mutant could support the growth of λ phage at 41 C. However, the λ phages thus produced were able to form plaques with normal plating efficiency only on E. coli C, a restriction-less strain, but not on E. coli K. Since the λ phages produced in the mutant at 30 C could form plaques equally well on both E. coli strains, it was concluded that the dnaD mutant has a temperature-sensitive modification phenotype. Furthermore, since the dnaD mutant allowed some growth of unmodified λ·C phages at 41 C but less at 30 C, the mutant is also temperature sensitive in restriction. The relationship, if any, between temperature-sensitive deoxyribonucleic acid synthesis and temperature-sensitive modification-restriction in the dnaD mutant is not known. Similar experiments were done with three dnaC mutants and one dnaA mutant. Two dnaC mutants were found to have altered restriction phenotypes at 41 C, but none of the mutants were defective in modification.     

Overexpression and purification of the recombinant Ca2+-binding protein, apoaequorin

The small, monomeric Ca2+-binding photoprotein, aequorin, emits blue light by an intramolecular reaction when mixed with Ca2+. The photoprotein is made up of coelenterazine and molecular oxygen, bound noncovalently to apoaequorin (apoprotein). The chemical steps leading to light emission, involving the oxidative degradation of coelenterazine, have been studied extensively, but little is known about the active site and how the molecule catalyzes the oxidation of coelenterazine. The three-dimensional structure of the protein has not been determined and therefore answers to these questions have remained unavailable. The present paper describes a procedure for preparing fairly large amounts of apoaequorin and aequorin for X-ray crystallographic studies. It consists of fusing the apoaequorin cDNA to the signal peptide coding sequence of the outer membrane protein A of Escherichia coli, which is under the control of the lipoprotein promoter. When the cDNA was expressed in E. coli, a large excess of the recombinant protein was produced and released into the culture medium. Purification of the protein was accomplished by acid precipitation and DEAE-cellulose chromatography. The procedure yielded 7.4 mg of recombinant apoaequorin with a purity greater than 95% from 200 ml of culture medium. On regeneration with coelenterazine, the recombinant aequorin was fully active with Ca2+.     

Particle size of airborne mouse crude and defined allergens

Laboratory animal allergy is a serious occupational diseases of many workers and scientists engaged in animal experimentation. Control measures depend upon characterization of allergens including airborne particles. This study measured the particle size of crude mouse urine and pelt aeroallergens generated in mouse housing rooms and compared them with mouse serum albumin, a defined major allergen. Allergens were detected by specific immunological methods. Most crude and defined allergens (74.5-86.4%) concentrated on a filter with a retention size greater than 7 microns. In distrubed air, allergen concentration increased 1.4 (albumin) to 5 (crude) fold and the proportion of small particles increased from 1.4% in calm air to 4.5% in distrubed air. This information on the generation and size distribution of aeroallergens will be important in the development of effective counter measures.     

Conformational equilibria of the L-iduronate residue in non-sulphated di-, tetra- and hexa-saccharides and their alditols derived from dermatan sulphate.

The conformation of the L-iduronate residue in non-sulphated di-, tetra- and hexa-saccharides and their alditol derivatives derived from rooster comb dermatan sulphate was investigated by 400 MHz 1H-n.m.r. spectroscopy. The ratio of conformational isomers is obtained by the average spin-spin coupling constants of a mixture of nearly isoenergetic conformers (1C4, 4C1 and 2S0). The non-reducing terminal L-iduronate residue in the tetrasaccharides (I-H-I-H and I-H-G-H) and their alditols (I-H-I-H-ol and I-H-G-H-ol) is in equilibrium with three conformers (1C4, 30%; 4C1, 40%; 2S0, 30%) of nearly equal population. Whereas the internal L-iduronate residue in the tetrasaccharides (I-H-I-H and G-H-I-H) exists as an equilibrium mixture of 1C4 (54%) and 2S0 (42-44%) conformers, that of their alditols (I-H-I-H-ol and G-H-I-H-ol) is in equilibrium between 2S0 conformer (66%) and 1C4 conformer (28%). The conformational population for the internal L-iduronate residue 2I in the hexasaccharide (3I-H-2I-H-1I-H) is also calculated and compared with that for the L-iduronate residue in native dermatan sulphate, which was calculated on the basis of the spin-spin coupling constants reported by Gatti, Casu, Torri & Vercellotti [(1979) Carbohydr. Res. 68, c3-c7].