Epitope analysis and molecular modeling reveal the topography of the C-terminal peptide of the beta-subunit of human chorionic gonadotropin.

Human chorionic gonadotropin (hCG) belongs to a family of heterodimeric glycoprotein hormones that share a common alpha-subunit and a hormone-specific beta-subunit. Among the gonadotropin beta-subunits, greater than 85% homology exists between lutropin (hLH)beta and hCGbeta in their first 114 amino acid residues. However, unlike hLHbeta, hCGbeta contains a 31-amino acid hydrophilic stretch at its carboxyl end (CTPbeta: C-terminal peptide). Although the crystal structure of deglycosylated hCG has been solved, the topography of CTPbeta remains unknown. In this study, we have attempted to define the topology of CTPbeta using mAb probes. We investigated three epitopes on hCGalpha, which are hidden in the hCGalphabeta dimer. However, these epitopes are not hidden in hLH, which has a similar subunit interface to that of hCG, but lacks CTPbeta. This suggested that these epitopes are not masked at the subunit interface of hLH or hCG. Hence, we hypothesized that, in the case of hCG, these epitopes are masked by the CTPbeta. Consistent with this view, several treatments of hCG that removed CTPbeta unmasked these epitopes and enhanced their reactivity with the corresponding mAbs. In order to localise the position of CTPbeta on the alpha-subunit, we used an epitope-mapping strategy [N. Venkatesh & G. S. Murthy (1997) J. Immunol. Methods 202, 173-182] based on differential susceptibility of epitopes to covalent modifications. This enabled us to predict the possible topography of CTPbeta. Further, we were also able to build a model of CTPbeta, completely independently of the epitope-mapping studies, using a homology-based modeling approach [S. Krishnaswamy, I. Lakshminarayanan & S. Bhattacharya (1995) Protein Sci. 4 (Suppl. 2), 86-97]. Results obtained from these two different approaches (epitope analysis and homology modeling) agree with each other and indicate that portions of CTPbeta are in contact with hCGalpha in the native hCG dimer.     

Chronic viral hepatitis C: management update

The management of chronic viral hepatitis C is evolving rapidly. Monotherapy with interferon, the accepted standard of treatment until recently, achieves only a modest sustained virological response rate of 15%. Combination treatment with alpha-2b interferon and ribavirin has been shown to increase sustained response rates to 40% in patients who have never been treated with interferon and to 50% in those who have relapsed following monotherapy with interferon. However, side effects, which have led to the discontinuation of combination treatment in a significant proportion of patients, must be carefully monitored. Treatment with interferon alpha-2b and ribavirin has now been approved in Canada, but the selection and monitoring of patients suitable for combination treatment requires special expertise. Although improvements in current therapeutic options may be possible with more frequent, higher doses or long-acting forms of interferon together with ribavirin, low sustained response rates (i.e., below 30%) for patients with hepatitis C virus genotype 1 emphasize the need for novel antiviral medications that will target the functional sites of the HCV genome.     

Variation in the diet of the viperine snake Natvix mama in relation to prey availability

The diet of the viperine snake was compared with food availability in the Ebro Delta, a wetland largely occupied by rice fields, in 1990 and 1991. Snake selection of prey type and size was studied seasonally and by snake group: males, females and immature snakes. Overall, feeding activity (percentage of individuals with prey and number of prey per stomach) increased with food availability. Diet analysis showed that viperine snakes mainly foraged on the green frog Rana perezi (adults and tadpoles) and the carp Cyprinus earpio. Conversely, viperine snakes rejected the mosquito fish Gambusia holbroki which is the most abundant species in autumn, when Natrix maura has a low feeding activity. Statistical comparisons between viperine snake diet and prey availability showed that males selected small carp, immature snakes selected tadpoles and, in spring, females selected frogs. The selection of small carp by males may reflect a sexual divergence of trophic niche related to sexual size dimorphism, as females are larger than males. As tadpoles are presumably easier to catch than fish, tadpole selection by immature individuals may reflect variance in capture abilities. In spring, the selection of frogs by females overlapped with vitellogenesis, suggesting that females compensate for the cost of reproduction by selecting green frogs, which have a greater biomass and higher energy content than fish. Carps eaten in spring were smaller than in summer. Moreover, in summer viperine snakes selected smaller carp than the available mean size. This divergent tendency between carp size selection and carp size availability reveals how seasonal diet shifts in prey size selection may be a response to an increase in prey size.     

β-Ar-ACETYL D-GALACTOSAMINIDASE IN BULK SEPARATED NEURONS AND NEUROPIL FROM RAT CEREBRAL CORTEX

Abstract— β- N -Acetyl D-galactosaminidase was studied in isolated neuronal and neuropil fractions from cerebral cortex and subcellular fractions derived from them. Although the enzyme activity evinced some latency properties, its subcellular distribution pattern was broader than that observed with other acid hydrolases. By contrast with nine other acid hydrolases, it was more active in neuropil than neuronal fractions (neuronal/neuropil activity ratio 0.63). This ratio was preserved in lysosomal subfractions derived from the isolated cell fractions. The data is taken as further evidence for the microheterogeneity of lysosomal particles from the brain.