Complex carbohydrate-lectin interaction at the interface: a model for cellular adhesion. I. Effect of vesicle size on the kinetics of aggregation between a fatty acid conjugate of lectin and a liposomal asialoganglioside

Two types of phospholipid vesicles capable of mutual recognition have been tailor-made to serve as a model system for the study of carbohydrate-mediated cellular adhesion. One of the vesicles contained a fatty acid conjugate of a galactose specific lectin (lectin vesicle) and the other an asialoganglioside with a reactive terminal galactose residue (galactose vesicle). The kinetics of aggregation of these two types of vesicles was followed by monitoring time-dependent change in turbidity. A 10-100-fold enhancement in the forward rate constant (kf ranging from 7.1 x 10(5) to 4.5 x 10(7) M-1.s-1 at 27 degrees C) was observed when compared with that for the lectin-galactose system in solution (kf being 4.5 x 10(5) M-1.s-1), reported in the literature. A study of the influence of vesicle size on the rate of aggregation showed that enhancement depended on the curvature of the galactose vesicle rather than the density of asialoganglioside suggesting a possible diffusion in the plane of the membrane. The ratio, kf/kd is found to be approx. 10(10) M-1 indicating that the formation of multiple bonds plays a role for stable adhesion.     

Reactivity of glycoconjugate in membrane system II: Can a neutral glycolipid function as lectin receptor in the presence of gangliosides in plasma membrane?

To examine how surface Potential controls the reactivity of glycoconjugates at cell surface, the interaction of galactose-sPecific lectinse.g. peanut agglutinin,Ricinus cummunis agglutinin with liPosomes bearing asialo GM₁ were studied in the Presence of varying amount of ganglioside mixture, GM_n. The Presence of 5% GM_n causes comPlete slowing down of PreciPitin reaction and thereby make carbohydrate moiety of asialo GM₁ comPletely inaccessiblei.e. ‘cryPtic’. In contrast the Presence of 1–2% GM_n enhances the aPParent rate and amPlitude of the PreciPitin reaction as surface Potential becomes more negative. The relevance of the findings has been discussed in relation to the exPression and involvement of the cell-surface sialic acid residues during develoPment and differentiation.     

Spatial pattern of freshwater habitats and their prioritization using additive partitions of beta diversity of inhabitant piscine assemblages in the Terai–Dooars ecoregion of Eastern Himalayas

Limnology - Underlying spatial and habitat attributes of a river network are crucial to comprehend the bio-spatial arrangements within it, the study of which suffers from a paucity of information....     

Comparative studies on kinetics of inhibition of protein synthesis in intact cells by ricin and conjugate of ricin B-chain with momordin

Cofilin is an actin-binding protein of low molecular weight which is widely distributed in eukaryotes and is deeply involved in the dynamics of actin assembly in the cytoplasm. The actin-binding ability of cofilin is inhibited by inositol phosphates (PIP2), and the PIP2- and actin-binding site(s) has been localized in residues W104 - M115 of the cofilin primary sequence (Yonezawa et al. 1991). In the present study, in order to further clarify the functional domains in cofilin molecule, we constructed expression vectors containing cDNAs of different size with deletion at the 3-region of the open reading frame. The truncated cofilin molecules produced in E. coli were purified and examined for their actin-binding and PIP2-binding ability. We found that the truncated cofilin molecule without C-terminal residues #100-#166 including the previously-described actin-binding site could be cross-linked with actin by EDC, a zero-length cross-linker. In addition, these truncated peptides as well as synthetic peptides corresponding to the N-terminal sequence of cofilin suppressed the inhibitory action of PIP2 on actin-cofilin interaction. These results strongly suggest that additional actin- and PIP2-binding sites exist in the N-terminal region of cofilin.     

Role of incidence function in vaccine-induced backward bifurcation in some HIV models

The phenomenon of backward bifurcation in disease models, where a stable endemic equilibrium co-exists with a stable disease-free equilibrium when the associated reproduction number is less than unity, has important implications for disease control. In such a scenario, the classical requirement of the reproduction number being less than unity becomes only a necessary, but not sufficient, condition for disease elimination. This paper addresses the role of the choice of incidence function in a vaccine-induced backward bifurcation in HIV models. Several examples are given where backward bifurcations occur using standard incidence, but not with their equivalents that employ mass action incidence. Furthermore, this result is independent of the type of vaccination program adopted. These results emphasize the need for further work on the incidence functions used in HIV models.     

Dynamic variable selection in SNP genotype autocalling from APEX microarray data

Background  

Single nucleotide polymorphisms (SNPs) are DNA sequence variations, occurring when a single nucleotide – adenine (A), thymine (T), cytosine (C) or guanine (G) – is altered. Arguably, SNPs account for more than 90% of human genetic variation. Our laboratory has developed a highly redundant SNP genotyping assay consisting of multiple probes with signals from multiple channels for a single SNP, based on arrayed primer extension (APEX). This mini-sequencing method is a powerful combination of a highly parallel microarray with distinctive Sanger-based dideoxy terminator sequencing chemistry. Using this microarray platform, our current genotype calling system (known as SNP Chart) is capable of calling single SNP genotypes by manual inspection of the APEX data, which is time-consuming and exposed to user subjectivity bias.     

Lectin binding to complex carbohydrate at the interface: a study by resonance energy transfer.

The binding affinity of the oligosaccharide moiety of a neutral glycosphingolipid, asialoGM1, towards Ricinus communis agglutinin (RCAI) was determined for the first time by fluorescence resonance energy transfer (RET). The asialoGM1 was incorporated into a phospholipid (DMPC) vesicle doped with dansylated DPPE and then titrated with an increasing amount of the galactose specific RCAI. The efficiency of RET was determined by a saturable increase in the quenching of 'donor' fluorescence, i.e. the 'trp' residue of RCAI, due to the energy transfer from the 'acceptor' dansyl group on the surface of the vesicle. The apparent binding constant was found to be in the range of 10(5)-10(6) M-1 at 27 degrees C.     

Cooperative nonenzymic base recognition--a study of interaction of oligoguanylic acid with poly C

The interaction between poly C and (Gp)_nG(n = 1,2) in dilute solution was investigated spectrophotometrically in 0.1M phosphate buffer pH 7.2 under conditions unfavorable for the formation of self-associated complexes of oligoguanylic acids. Two isosbestic points were observed when poly C was titrated gradually with GpGpG, one at 232–233 mμ(in the range of 0–33% poly C) and one around 238 mμ (in the range of 50–100% poly C). The melting temperature (T_m) of the 1:1 poly C: (Gp)nG complexes (n = 1,2) of varying concentration were determined. The equilibrium properties of the 1:1 complexes can be described by two interaction parameters, namely, (i) cooperative stacking interaction between the first nearest neighbor of the adsorbed oligomer, and (ii) intrinsic association constant of the adsorbed oligomer with its polymeric site, since the cooperative helix–coil transition particularly in the smaller oligonucleotide can be described by an “all or none” model. Based on such a model the enthalpy of stacking inteaction-dependent T_m values yielded directly the sum of the enthalpy of stacking interaction and of basepairing (which is dependent on the chain length of the oligomer) and the value of S, the stability constant of a G–C pair within a helix. The enthalpy of formation of G–C pair is then calculated as ?6.3 kcal/base pair either from the chain length dependent enthalpy term or from the temperature coefficient of S values. From the S value and the association constant of 1:1 GpGpGpC:GpCpCpC complex, other thermodynamic parameters such as nucleation parameter (β) and free energy of stacking interaction can be obtained.