Cloning and characterisation of hAps1 and hAps2, human diadenosine polyphosphate-metabolising Nudix hydrolases.
BACKGROUND
The human genome contains at least 18 genes for Nudix hydrolase enzymes. Many have similar functions to one another. In order to understand their roles in cell physiology, these proteins must be characterised.


RESULTS
We have characterised two novel human gene products, hAps1, encoded by the NUDT11 gene, and hAps2, encoded by the NUDT10 gene. These cytoplasmic proteins are members of the DIPP subfamily of Nudix hydrolases, and differ from each other by a single amino acid. Both metabolise diadenosine-polyphosphates and, weakly, diphosphoinositol polyphosphates. An apparent polymorphism of hAps1 has also been identified, which leads to the point mutation S39N. This has also been characterised. The favoured nucleotides were diadenosine 5',5"'-pentaphosphate (kcat/Km = 11, 8 and 16 x 10(3) M(-1) x s(-1) respectively for hAps1, hAps1-39N and hAps2) and diadenosine 5',5"'-hexaphosphate (kcat/Km = 13, 14 and 11 x 10(3) M(-1) x s(-1) respectively for hAps1, hAps1-39N and hAps2). Both hAps1 and hAps2 had pH optima of 8.5 and an absolute requirement for divalent cations, with manganese (II) being favoured. Magnesium was not able to activate the enzymes. Therefore, these enzymes could be acutely regulated by manganese fluxes within the cell.


CONCLUSIONS
Recent gene duplication has generated the two Nudix genes, NUDT11 and NUDT10. We have characterised their gene products as the closely related Nudix hydrolases, hAps1 and hAps2. These two gene products complement the activity of previously described members of the DIPP family, and reinforce the concept that Ap5A and Ap6A act as intracellular messengers.
Leslie
Nick R
NR
Division of Cell Signalling, School of Life Sciences, The University of Dundee, Dundee, DD1 5EH, UK. n.r.leslie@dundee.ac.uk
McLennan
Alexander G
AG
Safrany
Stephen T
ST
D017766:Acid Anhydride Hydrolases / Q000032:analysis / Q000235:genetics / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D002417:Cattle; D003001:Cloning, Molecular; D003600:Cytosol / Q000201:enzymology; D006801:Humans; D051379:Mice; D008969:Molecular Sequence Data; D011755:Pyrophosphatases / Q000032:analysis / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000096:biosynthesis; D016415:Sequence Alignment; D013379:Substrate Specificity; D014018:Tissue Distribution; D014960:X Chromosome; D000096964:Nudix Hydrolases
D017766:Acid Anhydride Hydrolases; D011755:Pyrophosphatases; D012333:RNA, Messenger; D000096964:Nudix Hydrolases; C469383:NUDT10 protein, human; C469382:NUDT11 protein, human; C075829:diadenosine polyphosphate hydrolase