Structural highlights
Function
[PPX_ECOLI] Degradation of inorganic polyphosphates. Orthophosphate is released progressively from the ends of polyphosphate of circa 500 residues long, while chains of circa 15 residues compete poorly with polyphosphate as substrate.
Evolutionary Conservation
Check, as determined by ConSurfDB. You may read the explanation of the method and the full data available from ConSurf.
Publication Abstract from PubMed
The Escherichia coli Ppx protein is an exopolyphosphatase that degrades long-chain polyphosphates in a highly processive reaction. It also hydrolyzes the terminal 5' phosphate of the modified nucleotide guanosine 5' triphosphate 3' diphosphate (pppGpp). The structure of Ppx has been determined to 1.9 A resolution by X-ray crystallography. The exopolyphosphatase is an ASKHA (acetate and sugar kinases, Hsp70, actin) phosphotransferase with an active site found in a cleft between the two amino-terminal domains. Analysis of the active site indicates that among the ASKHA phosphotranferases of known structure, Ppx is the closest to the ectonucleoside triphosphate diphosphohydrolases. A third domain forms a six-helix claw that is similar to the catalytic core of the eukaryotic cyclic nucleotide phosphodiesterases. Most of the 29 sulfate ions bound to the Ppx dimer occupy sites where the polyP chain likely binds. An aqueduct that passes through the enzyme provides a physical basis for the enzyme's high processivity.
Origin of exopolyphosphatase processivity: Fusion of an ASKHA phosphotransferase and a cyclic nucleotide phosphodiesterase homolog.,Alvarado J, Ghosh A, Janovitz T, Jauregui A, Hasson MS, Sanders DA Structure. 2006 Aug;14(8):1263-72. PMID:16905100[1]
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.
References
- ↑ Alvarado J, Ghosh A, Janovitz T, Jauregui A, Hasson MS, Sanders DA. Origin of exopolyphosphatase processivity: Fusion of an ASKHA phosphotransferase and a cyclic nucleotide phosphodiesterase homolog. Structure. 2006 Aug;14(8):1263-72. PMID:16905100 doi:http://dx.doi.org/10.1016/j.str.2006.06.009
