The carbohydrate-binding domain of Lafora disease protein targets Lafora polyglucosan bodies.
Lafora's disease (LD) is an autosomal recessive and fatal form of epilepsy with onset in late childhood or adolescence. One of the characteristic features of LD pathology is the presence of periodic acid-Schiff (PAS) positive Lafora inclusion bodies. Lafora bodies are present primarily in neurons, but they have also been found in other organs. Histochemical and biochemical studies have indicated that Lafora bodies are composed mainly of polysaccharides. The LD gene, EPM2A, encodes a 331 amino acid long protein named laforin that contains an N-terminal carbohydrate-binding domain (CBD) and a C-terminal dual-specificity phosphatase domain (DSPD). Here we demonstrate that the CBD of laforin targets the protein to Lafora inclusion bodies and this property could be evolutionarily conserved. We also tested in vitro the effects of five LD missense mutations on laforin's affinity to Lafora body. While the missense mutant W32G failed to bind to purified Lafora body, four other mutants (S25P, E28L, F88L, and R108C) did not show any effect on the binding affinity. Based on these observations we propose the existence of a laforin-mediated glycogen metabolic pathway regulating the disposal of pathogenic polyglucosan inclusions. This is the first report demonstrating a direct association between the LD gene product and the disease-defining storage product, the Lafora bodies.
Ganesh
Subramaniam
S
Department of Biological Sciences and Bioengineering, Indian Institute of Technology, Kanpur, India. sganesh@iitk.ac.in
Tsurutani
Naomi
N
Suzuki
Toshimitsu
T
Hoshii
Yoshinobu
Y
Ishihara
Tokuhiro
T
Delgado-Escueta
Antonio V
AV
Yamakawa
Kazuhiro
K
D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D050260:Carbohydrate Metabolism; D002645:Chickens; D017124:Conserved Sequence; D054637:Dual-Specificity Phosphatases; D005936:Glucans / Q000378:metabolism; D006801:Humans; D066298:In Vitro Techniques; D002479:Inclusion Bodies / Q000378:metabolism / Q000473:pathology; D020192:Lafora Disease / Q000235:genetics* / Q000378:metabolism* / Q000473:pathology; D051379:Mice; D018345:Mice, Knockout; D008969:Molecular Sequence Data; D009154:Mutation; D017434:Protein Structure, Tertiary; D017027:Protein Tyrosine Phosphatases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D054558:Protein Tyrosine Phosphatases, Non-Receptor; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid
D005936:Glucans; D011993:Recombinant Fusion Proteins; C083094:polyglucosan; D054637:Dual-Specificity Phosphatases; C491989:Epm2a protein, mouse; D017027:Protein Tyrosine Phosphatases; D054558:Protein Tyrosine Phosphatases, Non-Receptor; C114990:EPM2A protein, human