Primary structure of N-linked carbohydrate chains of calreticulin from spinach leaves.

Calreticulin is a multifunctional Ca2+-binding protein of the endoplasmic reticulum of most eukaryotic cells. The 56 kDa Calreticulin glycoprotein isolated from spinach (Spinacia oleracea L.) leaves was N-deglycosylated by PNGase-F digestion. The carbohydrate moiety was isolated by gel permeation chromatography and purified by high-pH anion-exchange chromatography. The fractions were investigated by 500 MHz H-1-NMR spectroscopy, in combination with monosaccharide analysis and fast-atom bombardment-mass spectrometry. The following carbohydrate structure could be established as the major component (Man(8)GlcNAc(2)): [GRAPHICS] Heterogeneity was demonstrated by the presence of two minor components being Man(7)GlcNAc(2) lacking a terminal residue (D-1 or D-3), compared to the major component. A. cross-reactivity with an antibody against the endoplasmic reticulum retention signal HDEL was also found.