Lectins facilitate calcium‐induced fusion of phospholipid vesicles containing glycosphingolipids

Abstract

Ca2+‐induced fusion of phospholipid vesicles containing globoside (GL‐4) or disialoganglioside (GDla) is several‐fold slower than the fusion of the pure phospholipid vesicles. Lectins specific for these glycosphingolipids, soybean agglutinin and wheat germ agglutinin, respectively, enhance the rate of fusion when added to the vesicle suspension before the introduction of Ca2+. The enhancement depends on the lectin concentration and the time of preincubation with the lectin. We propose that lectins facilitate membrane fusion by inducing intermembrane contact, which is the first step in the overall process of membrane fusion, or by laterally phase separating the inhibitory glycolipids.

Influence of glycophorin incorporation on calcium induced fusion of phosphatidylserine vesicles

“…It is of interest to compare our results with those obtained in recent studies on the effect of glycolipids on the Ca2+-induced fusion of acidic phospholipid-containing vesicles (Sundler & Wijkander, 1983;Düzgünes et al, 1984a). Incorporation of 5-10 mol % of several glycolipids into these vesicles drastically reduces the rate and extent of Ca2+-induced fusion and in certain cases even completely prevents it, as we report for the glycophorin-containing vesicles.…”

“…The influence of several factors, e.g., head-group composition of mixed phospholipid vesicles (Düzgünes et al, 1981a,b;, bilayer curvature (Nir et al, 1982), divalent cation specificity (Wilschut et al, 1981;Bentz et al, 1983), the incorporation of glycolipids in the phospholipid bilayer (Sundler & Wijkander, 1983; Düzgünes et al, 1984a;Hoekstra et al, 1985), lipid-phase separations f These investigations were carried out under the auspices of The Netherlands Foundation for Chemical Research (SON) with financial aid from The Netherlands Organization for the Advancement of Pure Research (ZWO). and membrane hydration (Hoekstra, 1982b), and ionotropic and thermotropic phase transitions (Düzgünes et al, 1984b), on fusion of in particular phosphatidylserine-(PS-)1 containing vesicles has been examined.…”

Agglutination and fusion of globoside GL-4 containing phospholipid vesicles mediated by lectins and calcium ion

“…In the case of PS vesicles, the formation of an anhydrous Ca2+/PS complex of specific stoichiometry, possibly serving as the trigger for membrane fusion, has been suggested (Ekerdt & Papahadjopoulos, 1982), while a similar proposal has been described for PA-containing vesicles (Sundler et al, 1981). Interestingly, the insertion of GL-4 into PS bilayers inhibits both the for- mation of the specific Ca2+/PS complex (Ekerdt & Papahadjopoulos, 1982) and fusion (Düzgünes et al, 1984). The observation that Ca2+ (in the absence of SBA) caused very little fusion of GL-4-containing PE/PA vesicles (Figure 3) suggests that, analogous to the PS system, the presence of the globoside prevented the formation of the specific and fusiontriggering Ca2+/PA complex.…”

Promotion and inhibition of vesicle fusion by polylysine

“…The results in Figure 6 and Table I indicate that polylysine has little effect, if any, on the rate constant of fusion per se, /¡,. In this sense the action of polylysine is similar to that of lectins (Düzgünes et al, 1984) and synexin (Creutz et al, 1979;Hong et al, 1981Hong et al, , 1982, which was shown to enhance the overall rate of vesicle fusion and to reduce the Ca2+ threshold concentration merely by promoting vesicle aggregation, i.e., increasing only Cj| values (Hong et al, 1983). Another confirmation to our conclusion is the fact that removal of polylysine after initiation of fusion does not alter significantly the rate of fusion, while the addition of EDTA terminates the process.…”