The structures of the trigonal crystal form of bovine beta-lactoglobulin variant A at pH 6.2, 7.1, and 8.2 have been determined by X-ray diffraction methods at a resolution of 2.56, 2. 24, and 2.49 A, respectively. The corresponding values for R (Rfree) are 0.192 (0.240), 0.234 (0.279), and 0.232 (0.277). The C and N termini as well as two disulfide bonds are clearly defined in these models. The glutamate side chain of residue 89 is buried at pH 6.2 and becomes exposed at pH 7.1 and 8.2. This conformational change, involving the loop 85-90, provides a structural basis for a variety of pH-dependent chemical, physical, and spectroscopic phenomena, collectively known as the Tanford transition.

IRF-3, a member of the interferon regulatory factor (IRF) family of transcription factors, functions as a molecular switch for antiviral activity. IRF-3 uses an autoinhibitory mechanism to suppress its transactivation potential in uninfected cells, and virus infection induces phosphorylation and activation of IRF-3 to initiate the antiviral responses. The crystal structure of the IRF-3 transactivation domain reveals a unique autoinhibitory mechanism, whereby the IRF association domain and the flanking autoinhibitory elements condense to form a hydrophobic core. The structure suggests that phosphorylation reorganizes the autoinhibitory elements, leading to unmasking of a hydrophobic active site and realignment of the DNA binding domain for transcriptional activation. IRF-3 exhibits marked structural and surface electrostatic potential similarity to the MH2 domain of the Smad protein family and the FHA domain, suggesting a common molecular mechanism of action among this superfamily of signaling mediators.

Renewable energy-driven methanol synthesis from CO2 and green hydrogen is a viable and key process in both the “methanol economy” and “liquid sunshine” visions. Recently, In2O3-based catalysts have shown great promise in overcoming the disadvantages of traditional Cu-based catalysts. Here, we report a successful case of theory-guided rational design of a much higher performance In2O3 nanocatalyst. Density functional theory calculations of CO2 hydrogenation pathways over stable facets of cubic and hexagonal In2O3 predict the hexagonal In2O3(104) surface to have far superior catalytic performance. This promotes the synthesis and evaluation of In2O3 in pure phases with different morphologies. Confirming our theoretical prediction, a novel hexagonal In2O3 nanomaterial with high proportion of the exposed {104} surface exhibits the highest activity and methanol selectivity with high catalytic stability. The synergy between theory and experiment proves highly effective in the rational design and experimental realization of oxide catalysts for industry-relevant reactions.

The formation of protein complexes between phosphorylated R-Smads and Smad4 is a central event in the TGF-beta signaling pathway. We have determined the crystal structure of two R-Smad/Smad4 complexes, Smad3/Smad4 to 2.5 angstroms, and Smad2/Smad4 to 2.7 angstroms. Both complexes are heterotrimers, comprising two phosphorylated R-Smad subunits and one Smad4 subunit, a finding that was corroborated by isothermal titration calorimetry and mutational studies. Preferential formation of the R-Smad/Smad4 heterotrimer over the R-Smad homotrimer is largely enthalpy driven, contributed by the unique presence of strong electrostatic interactions within the heterotrimeric interfaces. The study supports a common mechanism of Smad protein assembly in TGF-beta superfamily signaling.

The X-ray structure of bovine L L-lactoglobulin with the ligand 12-bromododecanoic acid as a model for fatty acids has been determined at a resolution of 2.23 A î in the trigonal lattice Z form. The ligand binds inside the calyx, resolving a long-standing controversy as to where fatty-acid like ligands bind. The carboxylate head group lies at the surface of the molecule, and the lid to the calyx is open at the pH of crystallization (pH 7.3), consistent with the conformation observed in ligand-free bovine L L-lactoglobulin in lattice Z at pH 7.1 and pH 8.2.z 1998 Federation of European Biochemical Societies.

Smad3 transduces the signals of TGF-βs, coupling transmembrane receptor kinase activation to transcriptional control. The membrane-associated molecule SARA (Smad Anchor for Receptor Activation) recruits Smad3 for phosphorylation by the receptor kinase. Upon phosphorylation, Smad3 dissociates from SARA and enters the nucleus, in which its transcriptional activity can be repressed by Ski. Here, we show that SARA and Ski recognize specifically the monomeric and trimeric forms of Smad3, respectively. Thus, trimerization of Smad3, induced by phosphorylation, simultaneously activates the TGF-β signal by driving Smad3 dissociation from SARA and sets up the negative feedback mechanism by Ski. Structural models of the Smad3/SARA/receptor kinase complex and Smad3/Ski complex provide insights into the molecular basis of regulation.

Transcriptional activation of interferon beta (IFN-beta), an antiviral cytokine, requires the assembly of IRF-3 and CBP/p300 at the promoter region of the IFN-beta gene. The crystal structure of IRF-3 in complex with CBP reveals that CBP interacts with a hydrophobic surface on IRF-3, which in latent IRF-3 is covered by its autoinhibitory elements. This structural organization suggests that virus-induced phosphoactivation of IRF-3 triggers unfolding of the autoinhibitory elements and exposes the same hydrophobic surface for CBP interaction. The structure also reveals that the interacting CBP segment can exist in drastically different conformations, depending on the identity of the associating transcription cofactor. The finding suggests a possible regulatory mechanism in CBP/p300, by which the interacting transcription factor can specify the coactivator's conformation and influence the transcriptional outcome.

The orphan nuclear receptor Nur77 is an immediate-early response gene whose expression is rapidly induced by various extracellular stimuli. The aims of this study were to study the role of Nur77 expression in the growth and survival of colon cancer cells and the mechanism by which Nur77 expression was regulated. We showed that levels of Nur77 were elevated in a majority of human colon tumors (9/12) compared to their nontumorous tissues and that Nur77 expression could be strongly induced by different colonic carcinogens including deoxycholic acid (DCA). DCA-induced Nur77 expression resulted in up-regulation of antiapoptotic BRE and angiogenic VEGF, and it enhanced the growth, colony formation, and migration of colon cancer cells. In studying the mechanism by which Nur77 was regulated in colon cancer cells, we found that β-catenin was involved in induction of Nur77 expression through its activation of the transcriptional activity of AP-1 (c-Fos/c-Jun) that bound to and transactivated the Nur77 promoter. Together, our results demonstrate that Nur77 acts to promote the growth and survival of colon cancer cells and serves as an important mediator of the Wnt/β-catenin and AP-1 signaling pathways.