Showing papers on "Purple acid phosphatases published in 2014"

A Heterobimetallic FeIIIMnII Complex of an Unsymmetrical Dinucleating Ligand: A Structural and Functional Model Complex for the Active Site of Purple Acid Phosphatase of Sweet Potato

Abstract: The heterodinuclear mixed-valence complex [FeMn(ICIMP)(OAc)(2)Cl] (1) {H2ICIMP = 2-(N-carboxylmethyl)-[N-(N-methylimidazolyl-2-methyl)aminomethyl]-[6-(N-isopropylmethyl)-[N-(N-methylimidazolyl-2-methyl)]aminomethyl-4-methylphenol], an unsymmetrical N4O2 donor ligand} has been synthesized and fully characterized by several spectroscopic techniques as well as by X-ray crystallography. The crystal structure of the complex reveals that both metal centers in 1 are six-coordinate with the chloride ion occupying the sixth coordination site of the Mn-II ion. The phenoxide moiety of the ICIMP ligand and both acetate ligands bridge the two metal ions of the complex. Mossbauer spectroscopy shows that the iron ion in 1 is high-spin Fe-III. Two quasi-reversible redox reactions for the complex, attributed to the (FeMnII)-Mn-III/(FeMnII)-Mn-II (at -0.67 V versus Fc/Fc(+)) and (FeMnII)-Mn-III/(FeMnIII)-Mn-III (at 0.84 V), were observed by means of cyclic voltammetry. Complex 1, with an Fe-III-Mn-II distance of 3.58 angstrom, may serve as a model for the mixed-valence oxidation state of purple acid phosphatase from sweet potato. The capability of the complex to effect organophosphate hydrolysis (phosphatase activity) has been investigated at different pH levels (5.5-11) by using bis(2,4-dinitrophenyl)phosphate (BDNPP) as the substrate. Density functional theory calculations indicate that the substrate coordinates to the Mn-II ion. In the transition state, a hydroxide ion that bridges the two metal ions becomes terminally coordinated to the Fe-III ion and acts as a nucleophile, attacking the phosphorus center of BDNPP with the concomitant dissociation of the leaving group.

Chlamydomonas reinhardtii has a small family of purple acid phosphatase homologue genes that are differentially expressed in response to phytate

Abstract: Purple acid phosphatases (PAPs) are metallophosphoesterase enzymes involved in the acquisition and recycling of phosphorus. PAP phytases from microorganisms and plants are responsible for the dephosphorylation of phytate. Phytate is the main storage form of phosphorus in plant seeds and constitutes the major form of organic phosphorus present in soil. Although some phosphatases have been studied in Chlamydomonas reinhardtii, no gene coding for PAPs have so far been characterized. In this study, six PAP homologue genes were identified and characterized in silico in C. reinhardtii (CrPAP1 to CrPAP6). A metallophosphoesterase domain including the seven conserved residues characteristic of PAP enzymes was found in all six CrPAPs. The phylogenetic tree comprising PAP homologue sequences from microalgae, plants, and animals showed nine major clades and CrPAPs resolved in four of them. A constitutive expression was found for CrPAP2, CrPAP3, CrPAP4, and CrPAP6 in all media tested, while CrPAP1 and CrPAP5 were induced by the addition of phytate in a medium without phosphate salts. Our results provide a starting point for further functional analysis of the CrPAP gene family, and the evaluation of their potential as phytases in C. reinhardtii.

Design, synthesis and testing of novel classes of inhibitors against metallo-β-lactamases: Towards drug leads to combat antibiotic resistance

Abstract: Overprescription of antibiotics is one of the causes of the increasing incidence of antibiotic resistance. Bacteria are constantly evolving and able to develop resistance to new antibiotics by producing b-lactamases, thus causing the standard treatments to be ineffective. Furthermore, genes for antibiotic resistance can be transferred between unrelated species. b-Lactamases are classified into serine-b-lactamases (SBLs) and metallo-b-lactamases (MBLs). Clavulanic acid is a well-known inhibitor that can effectively inhibit serine b-lactamases (SBLs). Nonetheless, society is in urgent need of metallo-b-lactamase (MBL) inhibitors as clinically approved inhibitors for MBLs are not yet available. IMP-1, a clinically significant MBL has been reported to cause antibiotic resistance associated with infections such as pneumonia and wound infections. IMP-1 shows the characteristics of MBLs with di-Zn ions in the active site. One of the zinc ions in IMP-1 is ligated by three imidazoles of histidines, while the other zinc ion is ligated by the carboxylate of an aspartic acid, the imidazole of a histidine and the thiolate of a cysteine. In this research, novel inhibitors against IMP-1 MBL were designed based on the excellent competitive inhibition properties of L-captopril and D-captopril, compound RS-4.2, and compound 5.1. Modelling studies were done by docking these newly designed molecules into IMP-1 enzyme (PDB code: 1JJT) using Molegro Virtual Docker (MVD) software. Thiolate group of the designed compounds was predicted to bind to both zinc ions and the carboxylate and amide carbonyl groups of the compounds were predicted to form hydrogen bond or electrostatic interactions with the amino acid residues of the IMP-1 active site. Due to these favourable interactions, the MVD software predicted that the designed compounds would have high inhibition potencies against the enzyme. Syntheses of the designed molecules were completed via esterification of the starting materials, coupling reaction and lastly hydrolysis to remove both methyl ester and thioester. Eight series of compounds were synthesised including L- and D-proline derivatives (thiols and dicarboxylic acids), D-captopril derivatives, pipecolinic acid derivatives, phenylglycine derivatives, 2-aminopyridine derivatives, 2-amino-6-picolinic acid derivatives and diaminobenzoic acid derivatives. All of the synthesised compounds including the novel inhibitors and their precursors were tested against freshly expressed and purified IMP-1 enzyme. The expression process includes transformation, inoculation, enzyme expression and cell harvesting. The enzyme was purified via two-steps purification by using SP-Sepharose cation exchange column and Sepharacyl S-200 gel filtration size exclusion column. The yield of the enzyme obtained was 12 mg per 2 litres of culture. Among the compounds synthesised in this study, thiols 2.1.1 n 2.1.3 (Ki = 2.2 p 0.6 to 9.9 p 4.2 mM) and compounds 5.2 n 5.4 (Ki = 2.1 p 0.8 to 4.3 p 2.0 mM) are the most potent compounds against IMP-1. All of the compounds tested inhibit IMP-1 by competitive inhibition mode except compounds 5.2 n 5.4, which uncompetitively inhibit the enzyme. Screening of compounds synthesised as purple acid phosphatase (PAP) inhibitors were also performed against IMP-1 enzyme since PAPs, similar to IMP-1, are metallohydrolases with two metal ions in the active site. Only compounds 6.10 and 6.14 are potent enough to be further tested for their Ki values determination. Compound 6.10 has low inhibition potency against IMP-1 and inhibits the enzyme by uncompetitive inhibition (Ki = 71 p 50 mM). Compound 6.14 inhibits IMP-1 competitively with a Ki value of 5.4 p 2.5 mM.

Asymmetric Zn(II) Complexes as Structural and Functional Models for GpdQ

Abstract: In order to generate more structurally relevant biomimetics for dinuclear metallohydrolases much effort has been devoted to the synthesis of asymmetric ligands. These ligands are considered to be more suitable models for the asymmetric coordination environment found in enzymatic systems.