An investigation of the inclusion complex of cyclomaltoheptaose (beta-cyclodextrin) with N-methylanthranilic acid in the solid state.

A 2:1 complex between cyclomaltoheptaose (beta-cyclodextrin) and N-methylanthranilic acid has been studied in the solid state. The inclusion complex belongs to the triclinic system (space group P1) with unit cell dimensions a=15.2773(15)A, b=15.4710(15)A, c=17.9627(18)A, alpha=99.632(5) degrees , beta=113.416(5) degrees , and gamma=102.818(5) degrees . The complex forms a head-to-head channel-type structure with the N-methylanthranilic acid lying between the beta-cyclodextrin groups in a sandwich fashion, which is held in place by an extensive hydrogen-bonding network between the cyclodextrin molecules.

Role of ligand substitution in ferrocytochrome c folding.

The ligand substitutions that occur during the folding of ferrocytochrome c [Fe(II)cyt c] have been monitored by transient absorption spectroscopy. The folding reaction was triggered by photoinduced electron transfer to unfolded Fe(III)cyt c in guanidine hydrochloride (GuHCl) solutions. Assignments of ligation states were made by reference to the spectra of the imidazole and methionine adducts of N-acetylated microperoxidase 8. At pH 7, the heme in unfolded Fe(II)cyt c is ligated by native His18 and HisX (X = 26, 33) residues. The native Met80 ligand displaces HisX only in the last stages of folding. The ferroheme is predominantly five-coordinate in acidic solution; it remains five-coordinate until the native methionine binds the heme to give the folded protein (the rate of the methionine binding step is 16 +/- 5 s-1 at pH 5, 3.2 M GuHCl). The evidence suggests that the substitution of histidine by methionine is strongly coupled to backbone folding.

Action site and cellular effects of cytotoxin VacA produced by Helicobacter pylori.

Cells treated with the VacA toxin from Helicobacter pylori develop large membrane-bound vacuoles that originate from the late endocytotic pathway. Using different experimental approaches, we showed that VacA can induce vacuoles by acting within the cell cytosol. Moreover, separation of VacA-induced vacuoles at an early stage of formation, using a novel isopycnic density ultracentrifugation method, allowed us to show that they resemble a hybrid compartment, containing elements of both late endosomes and lysosomes. Functional defects of the endocytotic pathway were also studied before any macroscopic vacuolation is evident. VacA-intoxicated cells degrade extracellular ligands with reduced efficiency and, at the same time, they secrete acidic hydrolases into the extracellular medium, normally sorted to lysosomes. All these findings indicate that VacA translocates into the cell cytosol where it causes a lesion of the late endosomal/lysosomal compartments, such that protein trafficking across this crucial cross-point is altered with consequences that may be relevant to the pathogenesis of gastroduodenal ulcers.

Ontogeny of Ia+ accessory cells in fetal and newborn rat lung.

In the adult mammalian lung, Ia+ dendritic cells (DC) constitute a significant population of immunologically potent accessory cells that are important in the regulation of immune responses to inhaled antigens. The newborn, in most species, displays an increased susceptibility to sensitization by inhaled antigens; whether an immaturity of pulmonary accessory cells is involved has not been determined. In the present study, the ontogeny and function of these cells were examined in fetal and newborn rats. Cells identified as DC in fetal and newborn rat lungs were Ia+, C11b+/-, OX41-, OX43-, W3/13-, W3/25-, and OX8-. They were characterized ultrastructurally by an eccentric, lobulated nucleus, a paucity of lysosomes, delicate cytoplasmic processes, and abundant membrane-associated Ia. Ia+ DC were first detected within the pulmonary mesenchyme at day 15 and by day 17 of gestation they were also present within the epithelium lining airways. The appearance of Ia+ DC preceded the migration of either T4 or T8 subclasses of T cells to the lung, the latter becoming significant only after birth, when the newborn was exposed to environmental antigens. In none of the fetal or newborn animals was Ia detected on alveolar type II cells. The accessory cell function of rat pulmonary DC, isolated from fetuses at 20 and 21 days of gestation and from newborns, was tested by an autologous mixed leukocyte reaction. At 20 and 21 days of gestation, pulmonary DC were 40 and 60% as effective, respectively, in stimulating cell proliferation in purified autologous adult splenic T cells as those isolated from adults.(ABSTRACT TRUNCATED AT 250 WORDS)