NAD-catabolizing ectoenzymes of Schistosoma mansoni

Abstract

Infection with schistosomes (blood flukes) can result in the debilitating disease schistosomiasis. These parasites survive in their host for many years, and we hypothesize that proteins on their tegumental surface, interacting with the host microenvironment, facilitate longevity. One such ectoenzyme - the nucleotide pyrophosphatase/phosphodiesterase SmNPP5 can cleave ADP (to prevent platelet aggregation) and NAD (likely preventing Treg apoptosis). A second tegumental ectoenzyme, the glycohydrolase SmNACE, also catabolizes NAD. Here, we undertake a comparative biochemical characterization of these parasite ectoenzymes. Both are GPI-linked and exhibit different optimal pH ranges. While SmNPP5 requires divalent cations, SmNACE does not. The Km values of the two enzymes for NAD at physiological pH differ: SmNPP5, Km=340µM±44; SmNACE, Km=49µM±4. NAD cleavage by each enzyme yields different products. SmNPP5 cleaves NAD to form nicotinamide mononucleotide (NMN) and AMP, whereas SmNACE cleaves NAD to generate nicotinamide (NAM) and adenosine diphosphate ribose (ADPR). Each enzyme can process the other’s reaction product. Thus, SmNACE cleaves NMN (to yield NAM and ribose phosphate) and SmNPP5 cleaves ADPR (yielding AMP and ribose phosphate). Metabolomic analysis of plasma containing adult worms supports the idea that these cleavage pathways are active in vivo. We hypothesize that a primary function of SmNPP5 is to cleave NAD to control host immune cell function and a primary function of SmNACE is to cleave NMN to generate the vital nutrient nicotinamide (vitamin B3) for convenient uptake by the worms. Chemical inhibition of one or both ectoenzymes could upset worm metabolism and control schistosome infection.

Metabolism of FAD, FMN and riboflavin (vitamin B2) in the human parasitic blood flukeSchistosoma mansoni

“…Multiple sequence alignment was generated using Clustal Omega. The SmFADS protein contains 2 major domains: an N-terminal molybdenum cofactor (MoCF) binding domain (MoCF-BD) (L 22 -I 182 ; highlighted in yellow in SmFADS) and a C-terminal phosphoadenosine phosphosulphate (PAPS) domain (E 312 –G 501 ; highlighted in green in SmFADS). Residues conserved in all six sequences are indicated with (*), amino acids with strongly similar properties are indicated with (:), amino acids with weakly similar properties are indicated with (.).…”

“…SmNPP5-mediated cleavage of NAD generates NMN and AMP 20 . SmNPP5 is a 458 amino acid, glycophosphatidylinositol (GPI)-linked glycoprotein that can additionally cleave ATP, ADP and ADPR 21,22 . We hypothesize here that SmNPP5 can also hydrolyze FAD.…”

Metabolism of FAD, FMN and riboflavin (vitamin B2) in the human parasitic blood fluke Schistosoma mansoni

“…SmNPP5-mediated cleavage of NAD generates nicotinamide mononucleotide (NMN) and adenosine monophosphate (AMP) [20]. SmNPP5 is a 458 amino acid, glycophosphatidylinositol (GPI)-linked glycoprotein that can additionally cleave adenosine triphosphate (ATP), adenosine diphosphate (ADP) and adenosine diphosphate ribose (ADPR) [21,22]. We hypothesize here that SmNPP5 can also hydrolyze FAD.…”