Processing Enzymes Involved in N-glycan Biosynthesis and Related Genes: the Golgi N-glycan Processing α-mannosidase II and α-mannosidase IIx

N-linked carbohydrate modification is found in many secretary and cell surface proteins. This post-translational modification is thought to be important for biological function of proteins in vivo. Recent gene knockout studies demonstrated biological function of glycoproteins, and revealed as yet unknown biosynthetic pathway of N-glycans. We have analyzed the functions of α-mannosidase II (MII) and α-mannosidase IIx (MX) in the mouse by targeted disruption of each gene, and demonstrated that enzymatic activity of either MII or MX enzymes is essential for N-glycan biosynthesis in vivo. Mutant mice lacking both enzymatic activities die shortly after birth owing to respiration failure, thus suggesting the essential role of complex-type N-glycan in the lung of neonates.