N-acetyl-D-glucosaminylphosphatidylinositol de-N-acetylase from Entamoeba histolytica: metal alters catalytic rates but not substrate affinity

PIG-L/GPI12 proteins are endoplasmic reticulum-resident membrane proteins involved in the second step of glycosylphosphatidylinositol anchor biosynthesis in eukaryotes. We show that the Entamoeba histolytica PIG-L protein is optimally active in the acidic pH range. The enzyme has an intrinsic low level of de-N-acetylase activity in the absence of metal and is significantly stimulated by divalent cations. Metal binding induces a large conformational change in the protein that appears to improve catalytic rates while not altering the affinity of the enzyme for its substrate.