Identification of a high affinity binding site for lipooligosaccharidic NodRm factors in the microsomal fraction of Medicago cell suspension cultures

Protease-sensitive binding sites for a 35S-labeled ligand corresponding to the major lipo-oligosaccharidic symbiotic signal of Rhizobium meliloti (NodRm factor), have been identified in the microsomal fraction of Medicago varia cell suspension culture extracts. Binding was reversible and saturable and tetra-N-acetyl chitotetraose was a poor competitor of NodRm binding. Scatchard analysis suggests the presence of a high affinity binding site, termed Nod factor binding site two (NFBS2), with a Kd of 1.9 nM, and perhaps a second site with an affinity (Kd of 70 nM) similar to that of a site (NFBS1) previously characterized in Medicago truncatula root extracts