Serendipitous Discovery and X-Ray Structure of a Human Phosphate Binding Apolipoprotein

Laboratoire de Cristallogenèse et Cristallographie des Protéines, Institut de Biologie Structurale JP EBEL, 38027 Grenoble, France.
Structure (Impact Factor: 5.62). 04/2006; 14(3):601-9. DOI: 10.1016/j.str.2005.12.012
Source: PubMed


We report the serendipitous discovery of a human plasma phosphate binding protein (HPBP). This 38 kDa protein is copurified with the enzyme paraoxonase. Its X-ray structure is similar to the prokaryotic phosphate solute binding proteins (SBPs) associated with ATP binding cassette transmembrane transporters, though phosphate-SBPs have never been characterized or predicted from nucleic acid databases in eukaryotes. However, HPBP belongs to the family of ubiquitous eukaryotic proteins named DING, meaning that phosphate-SBPs are also widespread in eukaryotes. The systematic absence of complete genes for eukaryotic phosphate-SBP from databases is intriguing, but the astonishing 90% sequence conservation between genes belonging to evolutionary distant species suggests that the corresponding proteins play an important function. HPBP is the only known transporter capable of binding phosphate ions in human plasma and may become a new predictor of or a potential therapeutic agent for phosphate-related diseases such as atherosclerosis.

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    • "The detailed information referring to the isolation and purification of X-DING-CD4, HPBP and pDING was previously reported [4], [7], [10], [34]. PfluDING protein was used in the form of a site-specific mutation (S32G), altering one of the phosphate-binding residues, and resulting in a protein purified by the same method as the wild-type protein [34]. "
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    ABSTRACT: Independent research groups reported that DING protein homologues isolated from bacterial, plant and human cells demonstrate the anti-HIV-1 activity. This might indicate that diverse organisms utilize a DING-mediated broad-range protective innate immunity response to pathogen invasion, and that this mechanism is effective also against HIV-1. We performed structural analyses and evaluated the anti-HIV-1 activity for four DING protein homologues isolated from different species. Our data show that bacterial PfluDING, plant p38SJ (pDING), human phosphate binding protein (HPBP) and human extracellular DING from CD4 T cells (X-DING-CD4) share high degrees of structure and sequence homology. According to earlier reports on the anti-HIV-1 activity of pDING and X-DING-CD4, other members of this protein family from bacteria and humans were able to block transcription of HIV-1 and replication of virus in cell based assays. The efficacy studies for DING-mediated HIV-1 LTR and HIV-1 replication blocking activity showed that the LTR transcription inhibitory concentration 50 (IC50) values ranged from 0.052-0.449 ng/ml; and the HIV-1 replication IC50 values ranged from 0.075-0.311 ng/ml. Treatment of cells with DING protein alters the interaction between p65-NF-κB and HIV-1 LTR. Our data suggest that DING proteins may be part of an innate immunity defense against pathogen invasion; the conserved structure and activity makes them appealing candidates for development of a novel therapeutics targeting HIV-1 transcription.
    PLoS ONE 08/2013; 8(8):e69623. DOI:10.1371/journal.pone.0069623 · 3.23 Impact Factor
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    • "Despite the isolation of a number of DING proteins that inhibit HIV-1 replication, their lack of known gene sequences has been a hindrance to research. The full amino acid sequence of HPBP has been identified from the crystal structure and mass spectrometry [19] but attempts to produce the recombinant protein through the use of synthetic genes have been unsuccessful due to insolubility. "
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    ABSTRACT: .Background: Anti-HIV-1 therapy depends upon multiple agents that target different phases of the viral replication cycle. Recent reports indicate that plant and human DING proteins are unique in targeting viral gene transcription as the basis of their anti-HIV-1 therapy. Two cloned DING genes from Pseudomonas were transiently expressed in human cells, and effects on NF-kappa B-mediated transcription, HIV-1 transcription, and HIV-1 replication were measured RESULTS: Both DING proteins elevated NF-kappa B-mediated transcription. In microglial cells, one protein, from P. aeruginosa PA14, suppressed HIV-1 transcription; the other protein, from P. fluorescens SBW25, was inactive. The PA14 DING protein also reduces HIV-1 replication in microglial cells. Structural differences between the two DING proteins highlight regions of the PA14 DING protein essential to the anti-HIV-1 activity, and may guide the design of therapeutic agents.
    Virology Journal 07/2013; 10(1):234. DOI:10.1186/1743-422X-10-234 · 2.18 Impact Factor
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    • "La capacité des protéines DING à fixer le phosphate a été clairement démontrée [6] [31], mais les liens entre cette capacité et les propriétés biologiques des protéines DING restent encore méconnus, même s'il semble que l'activité phosphatase de p27 sj et ses conséquences sur le cycle cellulaire y sont probablement liées [23]. L'affinité pour le phosphate de PfluDING et de HPBP a été évaluée respectivement à environ 1 μM [20] et à une valeur sub-micromolaire [6], des affinités similaires à celles des phosphate-SBP bactériennes [30] [32]. "
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    ABSTRACT: DING proteins comprise an intriguing phosphate-binding protein family present in all animal phyla. Five different DING representatives have been described in humans. Eukaryotic DING proteins are mostly involved in cellular processes such as cell cycle regulation, and also in pathological process such as rheumatoid arthritis and kidney stone formation. Although these proteins are ubiquitous in eukaryotes, no relevant locus or ORF has yet been found in sequenced genomes. This lack of sequence information has considerably hampered functional and structural studies of these proteins, and has required the use of novel and original techniques such as ab initio protein sequencing based on a combination of X-ray crystallography and mass spectrometry. Sub-Angstrom structural resolution has elucidated the molecular binding mechanism of phosphate ions by these high-affinity proteins. Immunohistochemical studies show that these proteins are present in a wide variety of mouse tissues. Some DING proteins, particularly human phosphate binding protein (HPBP), can inhibit HIV replication. This inhibition takes place at the transcriptional step, which is not targeted by any current antiretroviral drug. Initial studies suggest that HPBP warrants animal testing. This recent discovery opens new possibilities for the treatment of HIV infection.
    Bulletin de l'Académie nationale de médecine 03/2012; 196(3):693-703; discussion 704. · 0.22 Impact Factor
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