Design and synthesis of oligosaccharides that interfere with glycoprotein quality-control systems.
Calnexin (CNX) and its soluble homologue calreticulin (CRT) are lectin-like molecular chaperones that help newly synthesized glycoproteins to fold correctly in the rough endoplasmic reticulum (ER). To investigate the mechanism of glycoprotein-quality control, we have synthesized structurally defined high-mannose-type oligosaccharides related to this system. This paper describes the synthesis of the non-natural undecasaccharide 2 and heptasaccharide 16, designed as potential inhibitors of the ER quality-control system. Each possesses the key tetrasaccharide element (Glc1Man3) critical for the CNX/CRT binding, while lacking the pentamannosyl branch required for glucosidase II recognition. These oligosaccharides were evaluated for their ability to bind CRT by isothermal titration calorimetry (ITC). As expected, each of them had a significant affinity towards CRT. In addition, these compounds were shown to be resistant to glucosidase II digestion. Their activities in blocking the chaperone function of CRT were next measured by using malate dehydrogenase (MDH) as a substrate. Their inhibitory effects were shown to correlate well with their CRT-binding affinities, both being critically dependent upon the presence of the terminal glucose (Glc) residue.
Arai
Midori A
MA
RIKEN (The Institute of Physical and Chemical Research), 2-1 Hirosawa, Wako, Saitama 351-0198, Japan.
Matsuo
Ichiro
I
Hagihara
Shinya
S
Totani
Kiichiro
K
Maruyama
Jun-ichi
J
Kitamoto
Katsuhiko
K
Ito
Yukishige
Y
D037281:Calnexin; D037282:Calreticulin / Q000037:antagonists & inhibitors*; D015195:Drug Design; D004721:Endoplasmic Reticulum / Q000502:physiology; D006023:Glycoproteins / Q000737:chemistry*; D006801:Humans; D018832:Molecular Chaperones / Q000037:antagonists & inhibitors*; D009844:Oligosaccharides / Q000138:chemical synthesis / Q000494:pharmacology*; D017510:Protein Folding
D037282:Calreticulin; D006023:Glycoproteins; D018832:Molecular Chaperones; D009844:Oligosaccharides; D037281:Calnexin