The X-lectins: a new family with homology to the Xenopus laevis oocyte lectin XL-35.

The Xenopus laevis oocyte cortical granule lectin (XL35) has been studied in fertilization and embryonic development. Several nucleic acid sequences that predict proteins homologous to XL35 have since been reported in frog, human, mouse, lamprey, trout, ascidian worm. These proteins also showed high degrees of amino acid sequence homology to a common fibrinogen-like motif that may involve carbohydrate binding. Although their biological functions and carbohydrate binding specificities have not been studied in detail, this new family of lectins has common characteristics. Several independent studies on this new family of lectins strongly suggest that the lectins are expressed and stored in specialized vesicles that may be released upon the infection by pathogens. In addition, some family members have been shown to bind to oligosaccharides from bacterial pathogens. Therefore, this family of lectins likely participates in pathogen surveillance as part of the innate immune system. We propose the name X-lectin family for these homologs of XL35.