The amino-acid sequence of the glucose/mannose-specific lectin isolated from Parkia platycephala seeds reveals three tandemly arranged jacalin-related domains

A mannose/glucose-specific lectin was isolated from seeds of Parkia platyce phala, the most primitive subfamily of Leguminosae plants. The molecular ma ss of the purified lectin determined by mass spectrometry was 47 946 +/- 6 Da (by electrospray ionization) and 47 951 +/- 9 Da (by matrix-assisted las er-desoption ionization). The apparent molecular mass of the lectin in solu tions of pH in the range 4.5-8.5 determined by analytical ultracentrifugati on equilibrium sedimentation was 94 +/- 3 kDa, showing that the protein beh aved as a non-pH-dependent dimer. The amino-acid sequence of the Parkia lec tin was determined by Edman degradation of overlapping peptides. This is th e first report of the primary structure of a Mimosoideae lectin. The protei n contained a blocked N-terminus and a single, nonglycosylated polypeptide chain composed of three tandemly arranged homologous domains. Each of these domains shares sequence similarity with jacalin-related lectin monomers fr om Asteraceae, Convolvulaceae, Moraceae, Musaceae, Gramineae, and Fagaceae plant families. Based on this homology, we predict that each Parkia lectin repeat may display a beta prism fold similar to that observed in the crysta l structure of the lectin from Helianthus tuberosus. The P. platycephala le ctin also shows sequence similarity with stress- and pathogen-upregulated d efence genes of a number of different plants, suggesting a common ancestry for jacalin-related lectins and inducible defence proteins.