Binding of oxo-Cu2 clusters to ferric ion-binding protein A from Neisseria gonorrhoeae: a structural insight

ABCE1 selectively promotes HIF-1α transactivation of angiogenic gene expression

BACKGROUND

Copper (Cu), by inhibiting the factor inhibiting HIF-1 (FIH-1), promotes the transcriptional activity of hypoxia-inducible factor-1 (HIF-1).

OBJECTIVE

The present study was undertaken to understand the molecular mechanism by which Cu inhibits FIH-1.

METHODS

Human umbilical vein endothelial cells (HUVECs) were treated with dimethyloxalylglycine (DMOG) resulting in HIF-1α accumulation and the FIH-1 protein complexes were pulled down for candidate protein analysis. The metal binding sites were predicted by both MetalDetector V2.0 and Metal Ion-Binding Site Prediction Server, and then the actual ability to bind to Cu in vitro was tested by both Copper-Immobilized metal affinity chromatography (Cu-IMAC) and Isothermal Titration Calorimetry (ITC). Subsequently, subcellular localization was monitored by immunocytochemistry, GFP-fusion protein expression plasmid and Western blotting in the nuclear extract. The interaction of candidate protein with HIF-1α and FIH-1 was validated by Co-Immunoprecipitation (Co-IP). Finally, the effect of candidate protein on the FIH-1 structure and HIF-1α transcriptional activity was analyzed by the InterEvDock3 web server and real-time quantitative RT-PCR.

RESULTS

ATP-binding cassette E1 (ABCE1) was present in the FIH-1 complexes and identified as a leading Cu-binding protein as indicated by a number of possible Cu binding sites. The ability of ABCE1 to bind Cu was demonstrated in vitro. ABCE1 entered the nucleus along with FIH-1 under hypoxic conditions. Protein interaction analysis revealed that ABCE1 prevented FIH-1 to bind iron ions, inhibiting FIH-1 enzymatic activity. ABCE1 silencing suppressed the expression of Cu-dependent HIF-1 target gene BNIP3, not that of Cu-independent IGF-2.

CONCLUSION

The results demonstrate that ABCE1, as a Cu-binding protein, enters the nucleus under hypoxic conditions and inhibits FIH-1degradation of HIF-1α, thus promoting HIF-1 transactivation of angiogenic gene expression.

Structure and Metal Binding Properties of Chlamydia trachomatis YtgA

The obligate intracellular pathogen Chlamydia trachomatis is a globally significant cause of sexually transmitted bacterial infections and the leading etiological agent of preventable blindness. The first-row transition metal iron (Fe) plays critical roles in chlamydial cell biology, and acquisition of this nutrient is essential for the survival and virulence of the pathogen. Nevertheless, how C. trachomatis acquires Fe from host cells is not well understood, since it lacks genes encoding known siderophore biosynthetic pathways, receptors for host Fe storage proteins, and the Fe acquisition machinery common to many bacteria. Recent studies have suggested that C. trachomatis directly acquires host Fe via the ATP-binding cassette permease YtgABCD. Here, we characterized YtgA, the periplasmic solute binding protein component of the transport pathway, which has been implicated in scavenging Fe(III) ions. The structure of Fe(III)-bound YtgA was determined at 2.0-Å resolution with the bound ion coordinated via a novel geometry (3 Ns, 2 Os [3N2O]). This unusual coordination suggested a highly plastic metal binding site in YtgA capable of interacting with other cations. Biochemical analyses showed that the metal binding site of YtgA was not restricted to interaction with only Fe(III) ions but could bind all transition metal ions examined. However, only Mn(II), Fe(II), and Ni(II) ions bound reversibly to YtgA, with Fe being the most abundant cellular transition metal in C. trachomatis Collectively, these findings show that YtgA is the metal-recruiting component of the YtgABCD permease and is most likely involved in the acquisition of Fe(II) and Mn(II) from host cells.IMPORTANCE Chlamydia trachomatis is the most common bacterial sexually transmitted infection in developed countries, with an estimated global prevalence of 4.2% in the 15- to 49-year age group. Although infection is asymptomatic in more than 80% of infected women, about 10% of cases result in serious disease. Infection by C. trachomatis is dependent on the ability to acquire essential nutrients, such as the transition metal iron, from host cells. In this study, we show that iron is the most abundant transition metal in C. trachomatis and report the structural and biochemical properties of the iron-recruiting protein YtgA. Knowledge of the high-resolution structure of YtgA will provide a platform for future structure-based antimicrobial design approaches.

Inhibiting effects of common trivalent metal ions on transmembrane-type 2 matrix metalloproteinase

Transmembrane-type 2 matrix metalloproteinase (MT2-MMP) degrades connective extracellular matrix between cells and enables tumor cells to migrate and metastasize, making this substance a potential therapeutic target in various diseases. In this work, the interactions between MT2-MMP and common trivalent metal ions, including aluminum (Al³⁺) and ferrum (Fe³⁺) ions, were investigated. Enzymatic detection revealed that Al³⁺ and Fe³⁺ strongly inhibited the MT2-MMP. Fluorescence spectrography elucidated a static quenching interaction between the negatively charged amino acids on MT2-MMP and the inhibitory trivalent metal ions, indicating that a stable complex was formed between MT2-MMP and metal ions. In addition, fluorescence data and molecular modeling analysis of the binding characteristics revealed that one trivalent metal ion bound with a protein in the stable complex formation process. The potential inhibitory effect of Al³⁺ on MT2-MMP was further examined in an MT2-MMP-overexpressed cell line, HT1080, by using flow cytometry. As a result, Al³⁺ can promote HT1080 cell apoptosis in a micromolar concentration-dependent manner. This work illustrated that common trivalent metal ions can potentially inhibit MT2-MMP-related tumors.