In this paper we study the assembly, in vivo and in vitro, of a family of hexameric, heat-labile enterotoxins produced by diarrheagenic bacteria. The toxins, which consist of an A subunit and five B subunits, are assembled by a highly coordinated process that ensures secretion of the holotoxin complex. We show that (i) oxidation of cysteine residues in the B subunits is a prerequisite step for in vivo formation of B-subunit pentamers, (ii) reduction of dissociated B subunits in vitro abolishes their ability to reassemble, (iii) the kinetics of B-pentamer assembly inl vivo can be mimicked under defined conditions in vitro, (iv) A subunits cannot associate with fully assembled B pentamers in vitro, and (v) A subunits cause an 3-fold acceleration in the rate of B-subunit pentamerization in vivo, implying that A subunits play a coordinating role in the pathway of holotoxin assembly. The last finding is likely to be of general significance, since it provides a mechanism for preferentially excluding or favoring certain intermediates in the assembly of multisubunit proteins.

By systematically manipulating promoter and ribosome binding structures, plasmid copy number and the structure of the cholera toxin B (CTB) subunit gene, we were able to develop a plasmid expression system that, when used in conjunction with an optimized growth medium, provided yields of CTB approaching one gram per liter. The CTB protein which was secreted to > 95%, could readily be purified from the growth medium of a V. cholerae production strain and was shown to be immunologically indistinguishable from previously used vaccine preparations of native or recombinant CTB.

SummaryThe closely related B-subunits of cholera toxin (CTB) and Escherichia coli heat-labile enterotoxin (LTB) both bind strongly to GM1 ganglioside receptors but LTB can also bind to additional glycolipids and glycoproteins. A number of mutant CT B-subunits were generated by substituting CTB amino acids with those at the corresponding positions in LTB. These were used to investigate the influence of specific residues on receptor-binding specificity. A mutated CTB protein containing the first 25 residues of LTB in combination with LTB residues at positions 94 and 95, bound to the same extent as native LTB to both delipidized rabbit intestinal cell membranes, complex glycosphingolipids (polyglycosylceramides) and neolactotetraosylceramide, but not to non-GM1 intestinal glycosphingolipids. In contrast, when LTB amino acid substitutions in the 1-25 region were combined with those in the 75-83 region, a binding as strong as that of LTB to intestinal glycosphingolipids was observed. In addition, a mutant LTB with a single Gly-33→Asp substitution that completely lacked affinity for both GM1 and non-GM1 glycosphingolipids could still bind to receptors in the intestinal cell membranes and to polyglycosylceramides. We conclude that the extra, non-GM1 receptors for LTB consist of both sialylated and non-sialylated glycoconjugates, and that the binding to either class of receptors is influenced by different amino acid residues within the protein.

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In animals, colorful and conspicuous ornaments enhance individual attractiveness to potential mates, but are typically tempered by natural selection for crypsis and predator protection. In species where males compete for females, this can lead to highly ornamented males competing for mating opportunities with choosy females, and vice versa. However, even where males compete for mating opportunities, females may exhibit conspicuous displays. These female displays are often poorly understood and it may be unclear whether they declare mating intent, signal intrasexual aggression or form a target for male mate preference. We examined the function of the conspicuous dark eyes that female sand gobies temporarily display during courtship by experimentally testing if males preferred to associate with females with artificially darkened eyes and if dark eyes are displayed during female aggression. By observing interactions between a male and two females freely associating in an aquarium we also investigated in which context females naturally displayed dark eyes. We found that dark eyes were more likely to be displayed by more gravid females than less gravid females and possibly ahead of spawning, but that males did not respond behaviorally to dark eyes or prefer dark-eyed females. Females behaving aggressively did not display dark eyes. We suggest that dark eyes are not a signal per se but may be an aspect of female mate choice, possibly related to vision.

SUMMARYThe purpose of this study was to determine whether infectious herpes simplex virus type l (HSV-1) has tumorigenic properties and, if so, whether inhibition of the cytolytic replicative cycle of the virus after infection enhances tumour development. Eighty mice were subjected to repeated inoculation of HSV-1 on their upper lips after scarification, and systemic administration of acyclovir (ACV). 12-O-tetradecanoylphorbol 13-acetate (TPA) was used as the tumour promoter. The tumour incidence was compared to control groups each of 40 mice that were either not treated with ACV, not treated with TPA, not infected with HSV or only scarified. In the virus-infected group treated with ACV and TPA, 25~ of the animals developed tumours. In the HSVinfected group treated with TPA only, 25 ~ of the animals also developed tumours. The uninfected animals which were not treated with TPA developed tumours to a significantly lesser degree. In conclusion, the combined effects of HSV-1 and TPA, with or without ACV treatment, resulted in a significant increase in the number of tumours in comparison to the control groups.

An epidemiological statistical model was designed to identify women at low and high risk of developing endometrial cancer (EC). The model was based on a number of easily identified clinical factors such as hirsutism, parity, diabetes mellitus, body mass index (BMI) and smoking. A retrospectively collected series of 77 women aged 31 to 45 years with EC and a prospectively collected series of 122 women aged 43 to 70 years with EC were compared with 1409 controls. The participation frequencies in the two case materials were 83 and 87%, respectively. The series were examined by means of a questionnaire. In a stepwise multiple logistic regression analysis of the entire series the following variables were found to be significant; hirsutism, parity, BMI, diabetes mellitus and smoking.