Influence of UDP-GlcNAc 2-epimerase/ManNAc kinase mutant proteins on hereditary inclusion body myopathy.
Hereditary inclusion body myopathy (HIBM), a neuromuscular disorder, is caused by mutations in UDP-N-acetylglucosamine 2-epimerase/N-acetylmannosamine kinase (GNE), the key enzyme of sialic acid biosynthesis. To date, more than 40 different mutations in the GNE gene have been reported to cause the disease. Ten of them, representing mutations in both functional domains of GNE, were recombinantly expressed in insect cells (Sf9). Each of the mutants that was analyzed displayed a reduction in the two known GNE activities, thus revealing that mutations may also influence the function of the domain not harboring them. The extent of reduction strongly differs among the point mutants, ranging from only 20% reduction found for A631T and A631V to almost 80% reduction of at least one activity in D378Y and N519S mutants and more than 80% reduction of both activities of G576E, underlined by structural changes of N519S and G576E, as observed in CD spectroscopy and gel filtration analysis, respectively. We therefore generated models of the three-dimensional structures of the epimerase and the kinase domains of GNE, based on Escherichia coli UDP-N-acetylglucosamine 2-epimerase and glucokinase, respectively, and determined the localization of the HIBM mutations within these proteins. Whereas in the kinase domain most of the mutations are localized inside the enzyme, mutations in the epimerase domain are mostly located at the protein surface. Otherwise, the different mutations result in different enzymatic activities but not in different disease phenotypes and, therefore, do not suggest a direct role of the enzymatic function of GNE in the disease mechanism.
Penner
Juliane
J
Charité-Universitätsmedizin Berlin, Campus Benjamin Franklin, Institut für Biochemie und Molekularbiologie, Arnimallee 22, 14195 Berlin-Dahlem, Germany.
Mantey
Lars R
LR
Elgavish
Sharona
S
Ghaderi
Darius
D
Cirak
Sebahattin
S
Berger
Markus
M
Krause
Sabine
S
Lucka
Lothar
L
Voit
Thomas
T
Mitrani-Rosenbaum
Stella
S
Hinderlich
Stephan
S
D016367:Baculoviridae / Q000378:metabolism; D002238:Carbohydrate Epimerases / Q000235:genetics / Q000378:metabolism / Q000494:pharmacology; D006801:Humans; D008958:Models, Molecular; D009097:Multienzyme Complexes / Q000737:chemistry / Q000378:metabolism; D009154:Mutation; D018979:Myositis, Inclusion Body / Q000378:metabolism*; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000235:genetics / Q000378:metabolism / Q000494:pharmacology*; D017434:Protein Structure, Tertiary / Q000235:genetics; D021381:Protein Transport; D013329:Structure-Activity Relationship
D009097:Multienzyme Complexes; C482901:UDP-N-acetylglucosamine 2-epimerase - N-acetylmannosamine kinase; D017853:Phosphotransferases (Alcohol Group Acceptor); C018765:N-acylmannosamine kinase; D002238:Carbohydrate Epimerases; C100033:UDP acetylglucosamine-2-epimerase