title: Laforin, the dual-phosphatase responsible for Lafora disease, interacts with R5 (PTG), a regulatory subunit of protein phosphatase-1 that enhances glycogen accumulation.
abstract: Progressive myoclonus epilepsy of Lafora type (LD, MIM 254780) is a fatal autosomal recessive disorder characterized by the presence of progressive neurological deterioration, myoclonus, epilepsy and polyglucosan intracellular inclusion bodies, called Lafora bodies. Lafora bodies resemble glycogen with reduced branching, suggesting an alteration in glycogen metabolism. Linkage analysis and homozygosity mapping localized EPM2A, a major gene for LD, to chromosome 6q24. EPM2A encodes a protein of 331 amino acids (named laforin) with two domains, a dual-specificity phosphatase domain and a carbohydrate binding domain. Here we show that, in addition, laforin interacts with itself and with the glycogen targeting regulatory subunit R5 of protein phosphatase 1 (PP1). R5 is the human homolog of the murine Protein Targeting to Glycogen, a protein that also acts as a molecular scaffold assembling PP1 with its substrate, glycogen synthase, at the intracellular glycogen particles. The laforin-R5 interaction was confirmed by pull-down and co-localization experiments. Full-length laforin is required for the interaction. However, a minimal central region of R5 (amino acids 116-238), including the binding sites for glycogen and for glycogen synthase, is sufficient to interact with laforin. Point-mutagenesis of the glycogen synthase-binding site completely blocked the interaction with laforin. The majority of the EPM2A missense mutations found in LD patients result in lack of phosphatase activity, absence of binding to glycogen and lack of interaction with R5. Interestingly, we have found that the LD-associated EPM2A missense mutation G240S has no effect on the phosphatase or glycogen binding activities of laforin but disrupts the interaction with R5, suggesting that binding to R5 is critical for the laforin function. These results place laforin in the context of a multiprotein complex associated with intracellular glycogen particles, reinforcing the concept that laforin is involved in the regulation of glycogen metabolism.
authors.affiliation: Departamento de Inmunología, Centro de Investigaciones Biológicas, Consejo Superior de Investigaciones Científicas, Madrid, Spain.
authors.forename: Maria Elena
authors.initials: ME
authors.lastname: Fernández-Sánchez
authors.forename: Olga
authors.initials: O
authors.lastname: Criado-García
authors.forename: Karen E
authors.initials: KE
authors.lastname: Heath
authors.forename: Belén
authors.initials: B
authors.lastname: García-Fojeda
authors.forename: Iria
authors.initials: I
authors.lastname: Medraño-Fernández
authors.forename: Pilar
authors.initials: P
authors.lastname: Gomez-Garre
authors.forename: Pascual
authors.initials: P
authors.lastname: Sanz
authors.forename: José María
authors.initials: JM
authors.lastname: Serratosa
authors.forename: Santiago
authors.initials: S
authors.lastname: Rodríguez de Córdoba
mesh_terms: D000818:Animals; D019556:COS Cells; D002352:Carrier Proteins / Q000378:metabolism*; D054637:Dual-Specificity Phosphatases; D004926:Escherichia coli / Q000235:genetics; D005808:Genes, Recessive; D005822:Genetic Vectors; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D020192:Lafora Disease / Q000378:metabolism*; D051379:Mice; D010749:Phosphoprotein Phosphatases; D010957:Plasmids; D054645:Protein Phosphatase 1; D017027:Protein Tyrosine Phosphatases / Q000235:genetics / Q000378:metabolism*; D054558:Protein Tyrosine Phosphatases, Non-Receptor; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D014170:Transformation, Genetic
chemical_list: D002352:Carrier Proteins; D047908:Intracellular Signaling Peptides and Proteins; C491294:PPP1R3C protein, human; C104748:Ppp1r3c protein, mouse; D011993:Recombinant Fusion Proteins; D010749:Phosphoprotein Phosphatases; D054645:Protein Phosphatase 1; D054637:Dual-Specificity Phosphatases; C491989:Epm2a protein, mouse; D017027:Protein Tyrosine Phosphatases; D054558:Protein Tyrosine Phosphatases, Non-Receptor; C114990:EPM2A protein, human