Retinal ligatin recognizes glycoproteins bearing oligosaccharides terminating in phosphodiester-linked glucose.

Ligatin is a filamentous, baseplate protein that binds and localizes peripheral glycoproteins to the external cell surface. Glycoproteins coisolated with ligatin from embryonic chicken neural retina and radiolabeled with 32P are retained by an affinity column containing covalently bound retinal ligatin. Elution is achieved preferentially by alpha-glucose 1-phosphate and, to a limited extent, by mannose 6-phosphate. Treatment with endo-beta-N-acetylglucosaminidase H prevents the proteins from binding to the column and results in the release of high-mannose-type oligosaccharides containing 32P. The simplest of these oligosaccharides is unaffected by alkaline phosphatase unless the treatment is preceded by mild acid hydrolysis. Enzymatic and chemical analyses suggest that the phosphate is present in phosphodiester bonds linking penultimate mannose residues to terminal glucose residues.