Cloning and expression of 1,2-alpha-mannosidase gene (fmanIB) from filamentous fungus Aspergillus oryzae: in vivo visualization of the FmanIBp-GFP fusion protein.
1,2-alpha-Mannosidase catalyzes the specific cleavage of 1,2-alpha-mannose residues from protein-linked N-glycan. In this study, a novel DNA sequence homologous to the authentic 1,2-alpha-mannosidase was cloned from a cDNA library prepared from solid-state cultured Aspergillus oryzae. The fmanIB cDNA consisted of 1530 nucleotides and encoded a protein of 510 amino acids in which all consensus motifs of the class I alpha-mannosidase were conserved. Expression of the full length of 1,2-alpha-mannosidase cDNA by the Aspergillus host, though it has rarely been done with other filamentous-fungal mannosidase, was successful with fmanIB and caused an increase in both intracellular and extracellular mannosidase activity. The expressed protein (FmanIBp) specifically hydrolyzed 1,2-alpha-mannobiose with maximal activity at a pH of 5.5 and a temperature of 45 degrees C. With Man(9)GlcNAc(2) as the substrate, Man(5)GlcNAc(2) finally accumulated while hydrolysis of the 1,2-alpha-mannose residue of the middle branch was rate-limiting. To examine the intracellular localization of the enzyme, a chimeric protein of FmanIBp with green fluorescent protein was constructed. It showed a dotted fluorescence pattern in the mycelia of Aspergillus, indicative of the localization in intracellular vesicles. Based on these enzymatic and microscopic results, we estimated that FmanIBp is a fungal substitute for the mammalian Golgi 1,2-alpha-mannosidase isozyme IB. This and our previous report on the presence of another ER-type mannosidase in A. oryzae (Yoshida et al., 2000) support the notion that the filamentous fungus has similar steps of N-linked glycochain trimming to those in mammalian cells.
National Research Institute of Brewing, Hiroshima, Japan.
Takeshi
T
Akao
Masako
M
Yamaguchi
Akinori
A
Yahara
Kumi
K
Yoshiuchi
Hiroya
H
Fujita
Osamu
O
Yamada
Osamu
O
Akita
Tetsuo
T
Ohmachi
Yoshihiro
Y
Asada
Takashi
T
Yoshida
D000595:Amino Acid Sequence; D001236:Aspergillus oryzae / Q000737:chemistry* / Q000201:enzymology* / Q000235:genetics; D001483:Base Sequence; D003001:Cloning, Molecular; D015870:Gene Expression / Q000235:genetics*; D006031:Glycosylation; D008358:Mannose / Q000737:chemistry / Q000378:metabolism; D008361:Mannosidases / Q000235:genetics / Q000378:metabolism*; D008856:Microscopy, Fluorescence; D008969:Molecular Sequence Data; D008970:Molecular Weight; D010957:Plasmids / Q000235:genetics; D011134:Polysaccharides / Q000737:chemistry / Q000378:metabolism; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism
D011134:Polysaccharides; D011994:Recombinant Proteins; D008361:Mannosidases; C046090:mannosyl-oligosaccharide 1,2-alpha-mannosidase; D008358:Mannose