3typ
From Proteopedia
The crystal structure of the inorganic triphosphatase NE1496
Structural highlights
Function[3PASE_NITEU] Involved in the hydrolysis of the beta-gamma-phosphoanhydride linkage of triphosphate-containing substrates (inorganic or nucleoside-linked). Catalyzes the hydrolysis of inorganic triphosphate (PPPi). The enzyme has a strong preference for linear PPPi compared with cyclic PPPi (cyclic trimetaphosphate) and to the linear P4. The longer chains polyphosphate are not hydrolyzed. It has only a slight thiamine triphosphatase (ThTPase) activity. Nucleoside triphosphatase activity is negligible in the presence of magnesium, but a small activity is observed in the presence of manganese, in particular with GTP.[1] Publication Abstract from PubMedThe CYTH superfamily of proteins is named after its two founding members, the CyaB adenylyl cyclase from Aeromonas hydrophila and the human 25-kDa thiamine triphosphatase. Because these proteins often form a closed beta-barrel, they are also referred to as triphosphate tunnel metalloenzymes (TTM). Functionally, they are characterized by their ability to bind triphosphorylated substrates and divalent metal ions. These proteins exist in most organisms and catalyze different reactions depending on their origin. Here we investigate structural and catalytic properties of the recombinant TTM protein from Nitrosomonas europaea (NeuTTM), a 19-kDa protein. Crystallographic data show that it crystallizes as a dimer and that, in contrast to other TTM proteins, it has an open beta-barrel structure. We demonstrate that NeuTTM is a highly specific inorganic triphosphatase, hydrolyzing tripolyphosphate (PPP(i)) with high catalytic efficiency in the presence of Mg(2+). These data are supported by native mass spectrometry analysis showing that the enzyme binds PPP(i) (and Mg-PPP(i)) with high affinity (K(d) < 1.5 mum), whereas it has a low affinity for ATP or thiamine triphosphate. In contrast to Aeromonas and Yersinia CyaB proteins, NeuTTM has no adenylyl cyclase activity, but it shares several properties with other enzymes of the CYTH superfamily, e.g. heat stability, alkaline pH optimum, and inhibition by Ca(2+) and Zn(2+) ions. We suggest a catalytic mechanism involving a catalytic dyad formed by Lys-52 and Tyr-28. The present data provide the first characterization of a new type of phosphohydrolase (unrelated to pyrophosphatases or exopolyphosphatases), able to hydrolyze inorganic triphosphate with high specificity. A specific inorganic triphosphatase from Nitrosomonas europaea: structure and catalytic mechanism.,Delvaux D, Murty MR, Gabelica V, Lakaye B, Lunin VV, Skarina T, Onopriyenko O, Kohn G, Wins P, De Pauw E, Bettendorff L J Biol Chem. 2011 Sep 30;286(39):34023-35. Epub 2011 Aug 12. PMID:21840996[2] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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