title: Structural elucidation of a dual-activity PAP phosphatase-1 from Entamoeba histolytica capable of hydrolysing both 3'-phosphoadenosine 5'-phosphate and inositol 1,4-bisphosphate.
abstract: The enzyme 3'-phosphoadenosine 5'-phosphatase-1 (PAP phosphatase-1) is a member of the Li(+)-sensitive Mg(2+)-dependent phosphatase superfamily, or inositol monophosphatase (IMPase) superfamily, and is an important regulator of the sulfate-activation pathway in all living organisms. Inhibition of this enzyme leads to accumulation of the toxic byproduct 3'-phosphoadenosine 5'-phosphate (PAP), which could be lethal to the organism. Genomic analysis of Entamoeba histolytica suggests the presence of two isoforms of PAP phosphatase. The PAP phosphatase-1 isoform of this organism is shown to be active over wide ranges of pH and temperature. Interestingly, this enzyme is inhibited by submillimolar concentrations of Li(+), while being insensitive to Na(+). Interestingly, the enzyme showed activity towards both PAP and inositol 1,4-bisphosphate and behaved as an inositol polyphosphate 1-phosphatase. Crystal structures of this enzyme in its native form and in complex with adenosine 5'-monophosphate have been determined to 2.1 and 2.6 Å resolution, respectively. The PAP phosphatase-1 structure is divided into two domains, namely α+β and α/β, and the substrate and metal ions bind between them. This is a first structure of any PAP phosphatase to be determined from a human parasitic protozoan. This enzyme appears to function using a mechanism involving three-metal-ion assisted catalysis. Comparison with other structures indicates that the sensitivity to alkali-metal ions may depend on the orientation of a specific catalytic loop.
authors.affiliation: School of Life Sciences, Jawaharlal Nehru University, New Delhi 110 067, India.
authors.forename: Khaja
authors.initials: K
authors.lastname: Faisal Tarique
authors.affiliation: School of Life Sciences, Jawaharlal Nehru University, New Delhi 110 067, India.
authors.forename: Syed
authors.initials: S
authors.lastname: Arif Abdul Rehman
authors.affiliation: School of Life Sciences, Jawaharlal Nehru University, New Delhi 110 067, India.
authors.forename: S
authors.initials: S
authors.lastname: Gourinath
mesh_terms: D000244:Adenosine Diphosphate / Q000737:chemistry*; D015153:Blotting, Western; D018360:Crystallography, X-Ray; D004591:Electrophoresis, Polyacrylamide Gel; D004748:Entamoeba histolytica / Q000201:enzymology*; D005455:Fluorescent Antibody Technique; D006868:Hydrolysis; D007295:Inositol Phosphates / Q000737:chemistry*; D010744:Phosphoric Monoester Hydrolases / Q000737:chemistry*; D011487:Protein Conformation
chemical_list: D007295:Inositol Phosphates; C044259:inositol 1,4-bis(phosphate); D000244:Adenosine Diphosphate; C010840:adenosine 3'-phosphate-5'-phosphate; D010744:Phosphoric Monoester Hydrolases
keywords: Entamoeba histolytica; IMPase superfamily; PAP phosphatase; mobile catalytic loop