Title : Structure of mouse Golgi
alpha-mannosidase IA reveals the molecular basis for substrate specificity among class 1 (family
47 glycosylhydrolase ) alpha1,2-mannosidases
Abstract :
- Three subfamilies of mammalian Class 1 processing alpha1,2-mannosidases (family 47 glycosidases) play critical roles in the maturation of Asn-linked glycoproteins in the endoplasmic reticulum (ER) and Golgi complex as well as influencing the timing and recognition for disposal of terminally unfolded proteins by ER-associated degradation
- In an effort to define the structural basis for substrate recognition among Class 1 mannosidases, we have crystallized murine Golgi mannosidase IA (space group P 2(1 ) 2(1 ) 2(1 )), and the structure was solved to 1.5-A resolution by molecular replacement
- The enzyme assumes an (alphaalpha)(7) barrel structure with a Ca(2 +) ion coordinated at the base of the barrel similar to other Class 1 mannosidases
- Critical residues within the barrel structure that coordinate the Ca(2 +) ion or presumably bind and catalyze the hydrolysis of the glycone are also highly conserved
- A Man(6)GlcNAc(2) oligosaccharide attached to Asn(515) in the murine enzyme was found to extend into the active site of an adjoining protein unit in the crystal lattice in a presumed enzyme-product complex
- In contrast to an analogous complex previously isolated for Saccharomyces cerevisiae ER mannosidase I , the oligosaccharide in the active site of the murine Golgi enzyme assumes a different conformation to present an alternate oligosaccharide branch into the active site pocket
- A comparison of the observed protein-carbohydrate interactions for the murine Golgi enzyme with the binding cleft topologies of the other family 47 glycosidases provides a framework for understanding the structural basis for substrate recognition among this class of enzymes