Myxobacterial hemagglutinin: A development-specific lectin of Myxococcus xanthus

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Fruiting body formation in the bacterium Myxococcus xanthus consists of a temporal sequence of cellular aggregation and sporulation. During the period of cellular aggregation, a major new development-specific protein that has lectin-like activity is synthesized. This protein, called myxobacterial hemagglutinin (MBHA), was able to agglutinate sheep or guinea pig erythrocytes but not horse, ox, chicken, or human erythrocytes. MBHA was undetectable in extracts of vegetative cells, cells starved in liquid buffer, or in glycerol-induced cells. However, cells starved on a fruiting medium produced large amounts of MBHA (about 5% of protein synthesis), starting at about 6-8 hr of development. The protein accumulated in the soluble fraction of cells, reaching a peak of 1-2% of total protein at about the time when aggregation was completed. At later times the amount of MBHA present in the soluble fraction declined although synthesis continued. The hemagglutinating activity of MBHA could not be inhibited with simple sugars or aminosugars but could be inhibited with fetuin, a fetal calf serum glycoprotein. The O-glycosidically linked trisaccharide glycopeptide of fetuin was shown to be inhibitory by itself. The penultimate galactose of this glycopeptide was directly implicated in the inhibitory activity, because the inhibition by asialofetuin was reduced to 1/60th by periodate oxidation and to 1/15th after β-galactosidase treatment. MBHA is an abundant biochemical marker of development in M. xanthus. The fact that it is a lectin suggests that it may play a role in cell—cell recognition or agglutination.

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