Physarum polycephalum haemagglutinins: effect of nutrition on synthesis, and their possible role in nature

Abstract

The activity of haemagglutinins in plasmodia of Physanrm polycephalum was measured under different culture conditions. The activity was markedly increased when the plasmodia were incubated in a non-nutrient salt medium. During starvation, significant amounts of haemagglutinins were found in the slime layer on the surface of the plasmodia. An increase in activity was not observed in the presence of actinomycin D or cycloheximide. Under starvation conditions, plasmodia are known to differentiate into either sclerotia (spherules) or fruiting bodies. Acceleration of haemagglutinin synthesis, however, was not always observed during spherulation and fruiting-body formation. Attempts to detect endogenous glycoconjugates that bind to the haemagglutinins were unsuccessful but we found that the haemagglutinins could bind to acidic polysaccharides produced by Escherichia coli K12. The bacterial glycoconjugates were purified and partially characterized. They contained N-acetylhexosamine residues which appeared to be important for binding with the haemagglutinins. It is possible that the haemagglutinins play a physiological role in the interaction with these organisms.

Molecular analysis of Physarum haemagglutinin l: lack of a signal sequence, sulphur amino acids and post-translational modifications

“…It is likely that haemagglutinin I is also externalized by non-classical mechanisms and functions in some physiological events by interaction with glycoconjugates on the plasmodia1 surface. Because of its preferential binding to acidic polysaccharide from the bacterial cell wall, we assume that the function of haemagglutinin may be to interact with other organisms (Morita et al, 1995). In spite of several similarities, the amino acid sequence of haemagglutinin I is unrelated to those of fungal lectins and therefore represents a novel type of lectin.…”

“…Mushroom lectins in Flammulina uelutipes (Yatohgo et al, 1988) and Coprinus cinereus (Cooper et al, 1997) are developmentally regulated with high levels of expression in fruiting bodies and low levels of expression in vegetative mycelia, suggesting that these lectins may function in fruiting body formation. In P. polycephalum, however, it is unlikely that haemagglutinin I plays a role in the differentiation of plasmodia because acceleration of haemagglutinin synthesis was not always observed during macrocyst formation and fruiting body formation (Morita et al, 1995). Discoidin I, a lectin in the cellular slime mould D. discoideum, has an RGD sequence which participates in cell-substratum attachment (Barondes & Springer, 1987).…”

“…Purification of haemagglutinin I from microplasmodia was performed as described previously (Morita & Nishi, 1992). Haemagglutinating activity and haemagglutination inhibitory activity were measured with trypsin-treated, formalin-fixed rabbit erythrocytes as described previously (Morita et al, 1995).…”

“…These haemagglutinating activities were not inhibited by various monosaccharides but were strongly inhibited by thyroglobulin. We have also reported that an acidic polysaccharide from the bacterial cell wall might be a relevant ligand for haemagglutinin (Morita et al, 1995) and have hypothesized that Physarum haemagglutinins might play a physiological role in the interaction with bacteria in nature. However, the apparent role of haemagglutinins is not yet clear.…”

The Structure of Physarum polycephalum Hemagglutinin I Suggests a Minimal Carbohydrate Recognition Domain of Legume Lectin Fold

“…8 Although the physiological function of the secreted HA1 remains to be established, HA1 recognizes cell wall polysaccharides of E. coli. 10 As the name implies, HA1 agglutinates rabbit erythrocytes, which is inhibited in the presence of glycoproteins, orosomucoid, fetuin, and thyroglobulin. 8 Whereas periodate oxdation of the glycoproteins disrupts the binding of HA1 completely.…”