Dimeric quaternary structure of human laforin.

The phosphatase laforin removes phosphate groups from glycogen during biosynthetic activity. Loss of function mutations in the gene encoding laforin is the predominant cause of Lafora disease (LD), a fatal form of progressive myoclonic epilepsy. Here, we used hybrid structural methods to determine the molecular architecture of human laforin. We found that laforin adopts a dimeric quaternary structure, topologically similar to the prototypical dual specificity phosphatase (DSP) VH1. The interface between laforin carbohydrate-binding module (CBM) and DSP domain generates an intimate substrate-binding crevice that allows for recognition and dephosphorylation of phosphomonoesters of glucose. We identify novel molecular determinants in laforin active site that help decipher the mechanism of glucan phosphatase activity.