Binding properties of myxobacterial hemagglutinin

The nature of the receptor for myxobacterial hemagglutinin (MBHA) on the outer surface of Myxococcus xanthus was investigated by studying the binding of 125I-MBHA to vegetative and developmental cells. The amount of binding and hence the number of binding sites/cell appeared to increase 4-fold during development to 2.1 X 10(4) sites/cell. Furthermore, the apparent association constant (Ka) for MBHA increased 3-fold to 3 X 10(7) M-1. Fetuin, a glycoprotein which binds MBHA, blocked the binding of 125I-MBHA to vegetative cells but not developmental cells. Thus, the MBHA binding sites from developmental cells clearly differ from the vegetative binding sites. The Ka for MBHA binding to sheep erythrocytes (3.5 X 10(6) M-1) was an order of magnitude lower than that of developmental M. xanthus cells. The erythrocyte binding sites are also much more sensitive to concanavalin A inhibition than the M. xanthus sites.