The structure of bovine lysosomal alpha-mannosidase suggests a novel mechanism for low-pH activation.
Lysosomal alpha-mannosidase (LAM: EC 3.2.1.24) belongs to the sequence-based glycoside hydrolase family 38 (GH38). Two other mammalian GH38 members, Golgi alpha-mannosidase II (GIIAM) and cytosolic alpha-mannosidase, are expressed in all tissues. In humans, cattle, cat and guinea pig, lack of lysosomal alpha-mannosidase activity causes the autosomal recessive disease alpha-mannosidosis. Here, we describe the three-dimensional structure of bovine lysosomal alpha-mannosidase (bLAM) at 2.7A resolution and confirm the solution state dimer by electron microscopy. We present the first structure of a mammalian GH38 enzyme that offers indications for the signal areas for mannose phosphorylation, suggests a previously undetected mechanism of low-pH activation and provides a template for further biochemical studies of the family 38 glycoside hydrolases as well as lysosomal transport. Furthermore, it provides a basis for understanding the human form of alpha-mannosidosis at the atomic level. The atomic coordinates and structure factors have been deposited in the Protein Data Bank (accession codes 1o7d and r1o7dsf).
Heikinheimo
Pirkko
P
Institutt for Kjemi, Universitetet i Tromsø, N-9037, Tromsø, Norway.
Helland
Ronny
R
Leiros
Hanna-Kirsti Schrøder
HK
Leiros
Ingar
I
Karlsen
Solveig
S
Evjen
Gry
G
Ravelli
Raimond
R
Schoehn
Guy
G
Ruigrok
Rob
R
Tollersrud
Ole Kristian
OK
McSweeney
Seán
S
Hough
Edward
E
D000818:Animals; D001665:Binding Sites; D002417:Cattle; D018360:Crystallography, X-Ray; D019992:Databases as Topic; D019281:Dimerization; D004331:Drosophila melanogaster; D004789:Enzyme Activation; D006026:Glycoside Hydrolases / Q000737:chemistry; D006031:Glycosylation; D006860:Hydrogen Bonding; D006863:Hydrogen-Ion Concentration; D007668:Kidney / Q000201:enzymology; D008247:Lysosomes / Q000201:enzymology* / Q000378:metabolism; D008358:Mannose / Q000378:metabolism; D008361:Mannosidases / Q000737:chemistry*; D008854:Microscopy, Electron; D008958:Models, Molecular; D009154:Mutation; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D043323:alpha-Mannosidase
D006026:Glycoside Hydrolases; D008361:Mannosidases; D043323:alpha-Mannosidase; D008358:Mannose