THE BARK OF ROBINIA-PSEUDOACACIA CONTAINS A COMPLEX MIXTURE OF LECTINS - CHARACTERIZATION OF THE PROTEINS AND THE CDNA CLONES

Two lectins were isolated from the inner bark of Robinia pseudoacacia (black locust). The first (and major) lectin (called RPbAI) is compose d of five isolectins that originate from the association of 31.5- and 29-kD polypeptides into tetramers. In contrast, the second (minor) lec tin (called RPbAII) is a hometetramer composed of 26-kD subunits. The cDNA clones encoding the polypeptides of RPhAI and RPbAII were isolate d and their sequences determined. Apparently all three polypeptides ar e translated from mRNAs of approximately 1.2 kb. Alignment of the dedu ced amino acid sequences of the different clones indicates that the 31 .5- and 29-kD RPbAI polypeptides show approximately 80% sequence ident ity and are homologous to the previously reported legume seed lectins, whereas the 26-kD RPbAII polypeptide shows only 33% sequence identity to the previously described legume lectins. Modeling the 31.5-kD subu nit of RPbAI predicts that its three-dimensional structure is strongly related to the three-dimensional models that have been determined thu s far for a few legume lectins. Southern blot analysis of genomic DNA isolated from Robinia has revealed that the Robinia bark lectins are t he result of the expression of a small family of lectin genes.