Cell‐free synthesis and co‐translational processing of the human asialoglycoprotein receptor

The human asialoglycoprotein receptor is a 46‐kDa membrane glycoprotein. It is initially synthesized as a 40‐kDa precursor species possessing two N‐linked high‐mannose oligosaccharides which is subsequently converted to the 46‐kDa mature product upon modification of its oligosaccharides of the complex form [Schwartz, A. L. & Rup, D. (1983) J. Biol. Chem. 258, 11249–11255]. To investigate further the biosynthesis of the human asialoglycoprotein receptor, we have utilized a cell‐free wheat germ translation system supplemented with dog pancreatic microsomal membranes and programmed with HepG2 and human liver RNA. The primary translation product of the human receptor is a single 34‐kDa species and this species is expressed throughout human fetal and adult development. The primary translation product possesses no cleavable signal peptide and is co‐translationally glycosylated to form the 40‐kDa precursor species. In addition, the human asialoglycoprotein receptor is co‐translationally inserted into microsomal membranes such that a 4‐kDa cytoplasmic tail is susceptible to trypsin digestion.