Basic Study on Structure and Function of Mammalian Kidney Lectin.

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We have reported the partial purification and characterization of mammalian kidney lectins specific to sialic acid. Recently we have found the similar lectins also in chicken kidney. The common distribution of the kidney lectins in all the animals examined suggests that they play an importantrole in kidney specific functions. In this study, we developed new methods to detect and purify the kidney lectins and found their novel properties. In the new lectin detection method, the lectin sample was spotted on nitrocellulose membrane, washed with the solution of bovine serum albumin, reconstituted with phosphatidylethanolamine (PE), and allowed to react with horseradish peroxidase-labeled glycoproteins, and then the resulting binding was detected by coloration with diaminobenzidine. By this method the kidney extract devoid of lipids was found to bind strongly sialoglycoprotein only upon reconstitution with PE. Therefore, the inactivation of the lectins during purification procedures such as ion exchange chromatography and affinity chromatography could be explained by the removal of phospholipids essential for the lectin activity. One of the chicken lectins was recovered in fractions eluted with tris-buffered saline on hydrophobic chromatography using C18-Sepharose column and shown to contain several protein bands on SDS-PAGE analysis. When these bands were transfered to nitrocellulose membrane and examined by the new method, 31kDa protein was found to be a sialic acid specific lectin. furthermore, the lectin activity of the 31kDa protein was reactivated not only with PE, but also with PC, PI and PS. Therefore, the polar head group charge of phospholipids seemsnot to be directly concerned in the binding with sialic acid. It was also shown that the 31kDa protein has O<@D5-@>D5-linked oligosaccharides, and isoelectric point of <@DBca(/)-@>DDB.7, and its amino terminal blocked.