Synovial stimulatory protein fragments copurify with woodchuck hepatitis virus: implications for the etiology of arthritis in chronic hepatitis B virus infection

Shell Matrix Protein N38 of Pinctada fucata, Inducing Vaterite Formation, Extends the DING Protein to the Mollusca World

In the animal kingdom, DING proteins were only found in Chordata and Aschelminthes. At present study, a potential DING protein, matrix protein N38, was isolated and purified from the shell of Pinctada fucata. Tandem mass spectrometry analysis revealed that 14 peptide segments matched between N38 and human phosphate-binding protein (HPBP). HPBP belongs to the DING protein family and has a "DINGGG-" sequence, which is considered a "signature" of HPBP. In this study, the mass spectrometry analysis results showed that N38 had a "DIDGGG-" sequence; this structure is a mutation from the "DINGGG-" structure, which is a distinctive feature of the DING protein family. The role of N38 during calcium carbonate formation was explored through the in vitro crystallization experiment. The results of scanning electron microscopy and Raman spectrum analysis indicated that N38 induced vaterite formation. These findings revealed that N38 might regulate and participate in the precise control of the crystal growth of the shell, providing new clues for biomineralization mechanisms in P. fucata and DING protein family studies. In addition, this study helped extend the research of DING protein to the Mollusca world.

[Radiological differential diagnosis of rheumatoid arthritis]

CLINICAL/METHODICAL ISSUE

Establishing an early and reliable diagnosis of rheumatoid arthritis (RA) is of major importance but can be a great clinical challenge leading to direct therapeutic consequences. No single epidemiological, genetic, clinical, serological or radiological test exists which can exclusively diagnose RA.

STANDARD RADIOLOGICAL METHODS

In general diagnosis of RA includes a case history, clinical signs, laboratory abnormalities and radiological examinations, viz. conventional radiography of the joints of the hands and feet.

PRACTICAL RECOMMENDATIONS

This review summarizes the most important radiological features of RA and the radiological findings of its closest differential diagnoses.

Evidence for phosphatase activity of p27SJ and its impact on the cell cycle

p27SJ, a novel protein isolated from St John's wort (Hypericum perforatum), belongs to an emerging family of DING proteins that are related to a prokaryotic phosphate-binding protein superfamily. Here we demonstrate that p27SJ exhibits phosphatase activity and that its expression in cells decreases the level of phosphorylated Erk1/2, a key protein of several signaling pathways. Treatment of p27SJ-expressing cells with phosphatase inhibitors including okadaic acid, maintained Erk1/2 in its phosphorylated form, suggesting that dephosphorylation of Erk1/2 is mediated by p27SJ. Further, expression of p27SJ affects Erk1/2 downstream regulatory targets such as STAT3 and CREB. Moreover, the level of expression of cyclin A that associates with active ERK1/2 and is regulated by CREB, was modestly reduced in p27SJ-expressing cells. Accordingly, results from in vitro kinase assays revealed a noticeable decrease in the activity of cyclin A in cells expressing p27SJ. Cell cycle analysis demonstrated dysregulation at S and G2/M phases in cells expressing p27SJ, supporting the notion that a decline in cyclin A activity by p27SJ has a biological impact on cell growth. These observations provide evidence that p27SJ alters the state of Erk1/2 phosphorylation, and impacts several biological events associated with cell growth and function.

Identification of X-DING-CD4, a new member of human DING protein family that is secreted by HIV-1 resistant CD4(+) T cells and has anti-viral activity

We reported previously the anti-viral activity named HRF (HIV-1 Resistance Factor) secreted by HIV-1 resistant cells. This work describes the identification of HRF from cell culture supernatant of HRF-producing cells (HRF(+) cells). Employing the proteomics and cell based activity assay we recovered ten peptides sharing 80-93% sequence homology with other eukaryotic DING proteins; discrete amino acid characteristics found in our material suggested that HRF is a new member of DING proteins family and consequently we designated it as X-DING-CD4 (extracellular DING from CD4(+) T cells). The presence of X-DING-CD4 in the extracellular compartment of HRF(+) but not control HRF(-) cells was confirmed by specific anti-X-DING-CD4 antibody. Similar as the un-fractionated HRF(+) cell culture supernatant, the purified X-DING-CD4 blocked transcription of HIV-1 LTR-promoted expression of luciferase gene and replication of HIV-1 in MAGI cells. The X-DING-CD4 -mediated anti-viral activity in MAGI cells could be blocked by specific antibody.

For whom the bell tolls? DING proteins in health and disease

DING proteins, identified mainly by their eponymous N-terminal sequences, are ubiquitous in living organisms. Amongst bacteria, they are common in pseudomonads, and have been characterised with respect to genetics and structure. They form part of a wider family of phosphate-binding proteins, with emerging roles in phosphate acquisition and pathogenicity. Many DING proteins have been isolated in eukaryotes, in which they have been associated with very diverse biological activities, often in the context of possible signalling roles. Disease states in which DING proteins have been implicated include rheumatoid arthritis, lithiasis, atherosclerosis, some tumours and tumour-associated cachexia, and bacterial and viral adherence. Complete genetic and structural characterisation of eukaryotic DING genes and proteins is still lacking, though the phosphate-binding site seems to be conserved. Whether as bacterial proteins related to bacterial pathogenicity, or as eukaryotic components of biochemical signalling systems, DING proteins require further study.

The DING family of proteins: ubiquitous in eukaryotes, but where are the genes?

PstS and DING proteins are members of a superfamily of secreted, high-affinity phosphate-binding proteins. Whereas microbial PstS have a well-defined role in phosphate ABC transporters, the physiological function of DING proteins, named after their DINGGG N termini, still needs to be determined. PstS and DING proteins co-exist in some Pseudomonas strains, to which they confer a highly adhesive and virulent phenotype. More than 30 DING proteins have now been purified, mostly from eukaryotes. They are often associated with infections or with dysregulation of cell proliferation. Consequently, eukaryotic DING proteins could also be involved in cell-cell communication or adherence. The ubiquitous presence in eukaryotes of proteins structurally and functionally related to bacterial virulence factors is intriguing, as is the absence of eukaryotic genes encoding DING proteins in databases. DING proteins in eukaryotes could originate from unidentified commensal or symbiotic bacteria and could contribute to essential functions. Alternatively, DING proteins could be encoded by eukaryotic genes sharing special features that prevent their cloning. Both hypotheses are discussed.

Proteins related to St. John's Wort p27SJ, a suppressor of HIV-1 expression, are ubiquitous in plants

Proteins belonging to the family of DING proteins are ubiquitous in animals and several of them are associated with various diseases. Their presence in a few plant species has previously been reported and the St John's Wort DING protein was recently described as an inhibitor of HIV replication and transcription. However, data about DING protein occurrence in plants and their biochemical properties remain almost nonexistent. We describe methods for the purification of DING proteins from plants that may have general applicability since they are not dependent upon specific affinity ligands, contrary to previously described protocols. Cibacron Blue chromatography, sometimes preceded by an ion-exchange chromatographic step, is suitable for most plant extracts. DING proteins were purified from various species and cell types and their identity was confirmed immunologically and, in some cases, by N-terminal sequence analysis, indicating that they are ubiquitous in the plant kingdom. They are associated with the cell wall and sometimes secreted in the medium for in vitro grown cells. High-molecular-weight DING precursors were often observed. Internal peptides were also sequenced, as a prelude to gene cloning experiments.

DING proteins; novel members of a prokaryotic phosphate-binding protein superfamily which extends into the eukaryotic kingdom

PstS proteins are the cell-bound phosphate-binding elements of the ubiquitous bacterial ABC phosphate uptake mechanisms. Primary and tertiary structures, characteristic of pstS proteins, are conserved in proteins, which are expressed in secretory operons and induced by phosphate deprivation, in Pseudomonas species. There are two subsets of these proteins; AP proteins, which are alkaline phosphatases, and DING proteins, named for their N-terminal sequence, which are phosphate-binding proteins. Both form elements of a proposed phosphate-scavenging system in pseudomonads. DING proteins have also been isolated from many eukaryotic sources, and are associated with both normal and pathological functions in mammals. Their phosphate-binding function suggests a role in biomineralization, but the ability to bind other ligands may be related to signal transduction in eukaryotes. Though it has been claimed that all such proteins may originate from pseudomonads, many eukaryotic DING proteins have unique features which are incompatible with a bacterial origin.

Functional properties of a recombinant bacterial DING protein: comparison with a homologous human protein

DING proteins are highly-conserved proteins with poorly-defined cell-signalling roles in mammals. Conserved homologues are also commonplace in plants, though not as yet functionally characterized. Poor availability of the proteins, and a lack of genetic structure, hamper progress in elucidating the roles of these eukaryotic DING proteins, but highly-homologous hypothetical DING proteins have recently been identified in Pseudomonas genomes. We have cloned and expressed a DING protein from P. fluorescens SWB25 in Escherichia coli. The recombinant protein, and its natural human homologue, act as phosphate-binding proteins, as predicted by structural homologies with other bacterial proteins. The recombinant protein also displays other functional similarities with mammalian DING proteins, in that, like the human version, it acts as a mitogen for cultured human cells, and can bind cotinine, known to be a binding ligand for a rat neuronal DING protein.

Ring up the curtain on DING proteins

DING proteins have a characteristic DINGGG- or closely related N-terminal sequence. One is found in human synovial fluid, and may be associated with rheumatoid arthritis. Other examples have receptor or signalling roles in various human and animal cells, or are involved in biomineralisation, and several of them bind to phytochemicals. As plant DING proteins have recently been discovered, we hypothesise that the DING protein-phytochemical association may represent one aspect of a ubiquitous receptor-linked signalling system. Several microbial proteins related to DING proteins have phosphatase activity, which may relate to biomineralisation in eukaryotic systems. Plant DING proteins and their microbial relatives may elicit allergic responses leading to arthritic disease.