Oligosaccharide Specificities of Phaseolus vulgaris

The structural determinants required for interaction of oligosaccharides with leukoagglutinating phytohemagglutinin (L-PHA) and erythroagglutinating phytohemagglutinin (E-PHA) from Phaseolus vulgaris have been studied by immobilized lectin affinity chromatography. Homogeneous oligosaccharides of known structure, purified following release from Asn with Nglycanase and reduction with NaBH4, were tested for their ability to interact with columns of Land E-PHAagarose. The characteristic elution position obtained for each oligosaccharide was reproducible and correlated with specific structural features. In virtually all cases, Land E-PHA yielded identical results, indicating that their specificities for reduced oligosaccharides are similar. Both lectins retarded oligosaccharides bearing u2,3but not a2,6-linked sialic acid. Desialylated oligosaccharides containing one, two, three, or four peripheral N-acetyllactosamine-type branches were retarded to varying extents by both lectins; however, this interaction was decreased or eliminated by removal of Gal. Desialylated oligosaccharides containing a bisecting GlcNAc residue attached to the &linked core Man displayed the greatest interaction with both lectins. Structures containing terminal sulfate or GalNAc did not interact with either lectin. In some instances, the specificities of Land E-PHA lectins for free, reduced oligosaccharides differed from those established using glycopeptides. Therefore, the structural requirements for interaction with lectins such as Land E-PHA must be fully and systematically defined using the appropriate authentic standards in order to use lectin affinity chromatography for the fractionation and characterization of free oligosaccharides.