Crystal Structure of the Resuscitation-Promoting Factor ΔDUFRpfB from M. tuberculosis

Mycobacterium tuberculosis is able to establish a non-replicating state and survive in an intracellular habitat for years. Resuscitation of dormant M. tuberculosis bacteria is promoted by resuscitation-promoting factors (Rpfs), which are secreted from slowly replicating bacteria close to dormant bacteria. Here we report the crystal structure of a truncated form of RpfB (residues 194-362), the sole indispensable Rpf of the five Rpfs encoded in this bacterium genome. The structure, denoted as _ΔDUFRpfB, exhibits a comma-like shape formed by a lysozyme-like globular catalytic domain and an elongated G5 domain, which is widespread among cell surface binding proteins. The G5 domain, whose structure was previously uncharacterised, presents some peculiar features. The basic structural motif of this domain, which represents the tail of the comma-like structure, is a novel super-secondary-structure element, made of two β-sheets interconnected by a pseudo-triple helix. This intricate organisation leads to the exposure of several backbone hydrogen-bond donors/acceptors. Mutagenesis analyses and solution studies indicate that this protein construct as well as the full-length form are elongated monomeric proteins. Although _ΔDUFRpfB does not self-associate, the exposure of structural elements (backbone H-bond donors/acceptors and hydrophobic side chains) that are usually buried in globular proteins is typically associated with adhesive properties. This suggests that the RpfB G5 domain has a cell-wall adhesive function, which allows the catalytic domain to be properly oriented for the cleavage reaction. Interestingly, sequence comparisons indicate that these structural features are also shared by G5 domains involved in biofilm formation.     

Insulin-Like Growth Factor I (IGF-1) Ec/Mechano Growth Factor – A Splice Variant of IGF-1 within the Growth Plate

Human insulin-like growth factor 1 Ec (IGF-1Ec), also called mechano growth factor (MGF), is a splice variant of insulin-like growth factor 1 (IGF-1), which has been shown in vitro as well as in vivo to induce growth and hypertrophy in mechanically stimulated or damaged muscle. Growth, hypertrophy and responses to mechanical stimulation are important reactions of cartilaginous tissues, especially those in growth plates. Therefore, we wanted to ascertain if MGF is expressed in growth plate cartilage and if it influences proliferation of chondrocytes, as it does in musculoskeletal tissues. MGF expression was analyzed in growth plate and control tissue samples from piglets aged 3 to 6 weeks. Furthermore, growth plate chondrocyte cell culture was used to evaluate the effects of the MGF peptide on proliferation. We showed that MGF is expressed in considerable amounts in the tissues evaluated. We found the MGF peptide to be primarily located in the cytoplasm, and in some instances, it was also found in the nucleus of the cells. Addition of MGF peptides was not associated with growth plate chondrocyte proliferation.     

Transforming Growth Factor β Regulates P-Body Formation through Induction of the mRNA Decay Factor Tristetraprolin

Transforming growth factor β (TGF-β) is a potent growth regulator and tumor suppressor in normal intestinal epithelium. Likewise, epithelial cell growth is controlled by rapid decay of growth-related mRNAs mediated through 3′ untranslated region (UTR) AU-rich element (ARE) motifs. We demonstrate that treatment of nontransformed intestinal epithelial cells with TGF-β inhibited ARE-mRNA expression. This effect of TGF-β was promoted through increased assembly of cytoplasmic RNA processing (P) bodies where ARE-mRNA localization was observed. P-body formation was dependent on TGF-β/Smad signaling, as Smad3 deletion abrogated P-body formation. In concert with increased P-body formation, TGF-β induced expression of the ARE-binding protein tristetraprolin (TTP), which colocalized to P bodies. TTP expression was necessary for TGF-β-dependent P-body formation and promoted growth inhibition by TGF-β. The significance of this was observed in vivo, where colonic epithelium deficient in TGF-β/Smad signaling or TTP expression showed attenuated P-body levels. These results provide new insight into TGF-β''s antiproliferative properties and identify TGF-β as a novel mRNA stability regulator in intestinal epithelium through its ability to promote TTP expression and subsequent P-body formation.     

JIPB’s 2016 Impact Factor

正We are delighted to announce that JIPB's 2-year SCI impact factor(IF)has reached 3.962(8%increase as compared to last year,Fig.1),and 5-year IF is 3.956,according to 2016 Journal Citation Report.Among 211 SCI-indexed Plant Science journals in the world,JIPB ranks 24th(top 9.95%,Q1 category).The total citations of JIPB in 2016 are 3,773(12%increase as compared     

Engineering of Substrate Selectivity for Tissue Factor·Factor VIIa Complex Signaling through Protease-activated Receptor 2

The complex of factor VIIa (FVIIa) with tissue factor (TF) triggers coagulation by recognizing its macromolecular substrate factors IX (FIX) and X (FX) predominantly through extended exosite interactions. In addition, TF mediates unique cell-signaling properties in cancer, angiogenesis, and inflammation that involve proteolytic cleavage of protease-activated receptor 2 (PAR2). PAR2 is cleaved by FVIIa in the binary TF·FVIIa complex and by FXa in the ternary TF·FVIIa·FXa complex, but physiological roles of these signaling complexes are incompletely understood. In a screen of FVIIa protease domain mutants, three variants (Q40A, Q143N, and T151S) activated macromolecular coagulation substrates and supported signaling of the ternary TF·FVIIa-Xa complex normally but were severely impaired in binary TF·FVIIa·PAR2 signaling. The residues identified were located in the model-predicted S2′ pocket of FVIIa, and complementary PAR2 P2′ Leu-38 replacements demonstrated that the P2′ side chain was indeed crucial for PAR2 cleavage by TF·FVIIa. In addition, PAR2 was activated more efficiently by FVIIa T99Y, consistent with further contributions from the S2 subsite. The P2 residue preference of FVIIa and FXa predicted additional PAR2 mutants that were efficiently activated by TF·FVIIa but resistant to cleavage by the alternative PAR2 activator FXa. Thus, contrary to the paradigm of exosite-assisted cleavage of PAR1 by thrombin, the cofactor-associated protease FVIIa recognizes PAR2 predominantly by catalytic cleft interactions. Furthermore, the delineated molecular details of this substrate interaction enabled protein engineering of protease-selective PAR2 receptors that will aid further studies to dissect the roles of TF signaling complexes in vivo.