THE 67-KDA LAMININ RECEPTOR ORIGINATED FROM A RIBOSOMAL-PROTEIN THAT ACQUIRED A DUAL FUNCTION DURING EVOLUTION

The 67-kDa laminin receptor (67LR) is a nonintegrin cell surface recep tor that mediates high-affinity interactions between cells and laminin . Overexpression of this protein in tumor cells has been related to tu mor invasion and metastasis. Thus far, only a full-length gene encodin g a 37-kDa precursor protein (37LRP) has been isolated. The finding th at the cDNA for the 37LRP is virtually identical to a cDNA encoding th e ribosomal protein p40 has suggested that 37LRP is actually a compone nt of the translational machinery, with no laminin-binding activity. O n the other hand, a peptide of 20 amino acids deduced from the sequenc e of 37LRP/p40 was shown to exhibit high laminin-binding activity. The evolutionary relationship between 23 sequences of 37LRP/p40 proteins was analyzed. This phylogenetic analysis indicated that all of the pro tein sequences derive from orthologous genes and that the 37LRP is ind eed a ribosomal protein that acquired the novel function of laminin re ceptor during evolution. The evolutionary analysis of the sequence ide ntified as the laminin-binding site in the human protein suggested tha t the acquisition of the laminin-binding capability is linked to the p alindromic sequence LMWWML, which appeared during evolution concomitan tly with laminin.