There are currently two distinct models proposed to explain why both MDM2 and MDMX are required in p53 control, with a key difference centered on whether these two p53 inhibitors work together or independently. To test these two competing models, we generated knockin mice expressing a point mutation MDMX mutant (C462A) that is defective in MDM2 binding. This approach allowed a targeted disassociation of the MDM2/MDMX heterocomplex without affecting the ability of MDMX to bind to p53, and while leaving the MDM2 protein itself completely untouched. Significantly, Mdmx C462A/C462A homozygous mice died at approximately day 9.5 of embryonic development, as the result of a combination of apoptosis and decreased cell proliferation, as shown by TUNEL and BrdU incorporation assays, respectively. Interestingly, even though the MDMX mutant protein abundance was found slightly elevated in the Mdmx C462A/C462A homozygous embryos, both the abundance and activity of p53 were markedly increased. A p53-dependent death was demonstrated by the finding that concomitant deletion of p53 completely rescued the embryonic lethality in Mdmx C462A/C462A homozygous mice. Our data demonstrate that MDM2 and MDMX function as an integral complex in p53 control, providing insights into the nonredundant nature of the function of MDM2 and MDMX.knockin mouse model | p53 regulation U nder normal physiological conditions, wild-type p53 protein levels must be kept low owing to its growth-inhibitory activities, and this control is mainly modulated via regulation of p53 protein stability. Although a number of different regulators have been reported to be involved in this protein regulation, MDM2 has been shown to be the principal player in control of p53 turnover (1). MDM2 primarily functions as an E3 ubiquitin ligase targeting p53 for ubiquitination and subsequent degradation. At the same time, p53 induces the expression of the Mdm2 gene, forming a negative feedback loop (1). The importance of MDM2 in p53 control is highlighted by the finding that Mdm2 knockout results in p53-dependent embryonic lethality in mice (2, 3).MDMX (also known as MDM4), which was originally isolated as a novel p53-interacting protein, shares substantial structural homology with MDM2 (4, 5). The highest sequence similarity between MDM2 and MDMX lies at the N terminus and contains a p53-binding domain, and the two also share high sequence homology in a RING-finger domain, a region that mediates the association between MDMX and MDM2 (6,7). Genetic studies have demonstrated that like MDM2, MDMX is another essential negative regulator of p53 (8-10). Although it remains unclear why both MDM2 and MDMX are required for p53 control, a model has been proposed that these two proteins function independently. On the basis of the fact that unlike MDM2, MDMX lacks an intrinsic ubiquitin E3 ligase activity, it has been proposed that MDMX inhibits p53 chiefly by binding to the p53 transactivation domain and antagonizing p53 transcription activity, whereas MDM2 inactivates p53 primarily by wo...

Here we report a visible light-triggered, catalyst free bioorthogonal reaction that proceeds via a distinct pathway from reported bioorthogonal reactions. The prototype of this bioorthogonal reaction was the photocycloaddition of 9,10-phenanthrenequinone with electron-rich alkenes to form fluorogenic [4+2] cycloadducts. The bioorthogonal photoclick cycloaddition was readily initiated using a conventional visible light source such as a hand-held LED lamp. The reaction proceeded rapidly under biocompatible conditions, without observable competition from side reactions such as nucleophilic additions by water or common nucleophilic species. The bioorthogonal functionality in this reaction did not cross react with various alkynes and electron-deficient alkenes such as monomethyl fumarate. We demonstrated orthogonal labeling of two proteins using this reaction together with a strain promoting azide−alkyne click reaction or the UV-triggered reaction of tetrazole with monomethyl fumarate. The application of this reaction in the temporal and spatial labeling of live cells was also demonstrated.Communication pubs.acs.org/JACS

Ferrihydrite (Fh) supported Pt (Pt/Fh) catalyst was first prepared by combining microemulsion and NaBH4 reduction methods and investigated for room-temperature removal of formaldehyde (HCHO). It was found that the order of addition of Pt precursor and ferrihydrite in the preparation process has an important effect on the microstructure and performance of the catalyst. Pt/Fh was shown to be an efficient catalyst for complete oxidation of HCHO at room temperature, featuring higher activity than magnetite supported Pt (Pt/Fe3O4). Pt/Fh and Pt/Fe3O4 exhibited much higher catalytic activity than Pt supported over calcined Fh and TiO2. The abundance of surface hydroxyls, high Pt dispersion and excellent adsorption performance of Fh are responsible for superior catalytic activity and stability of the Pt/Fh catalyst. This work provides some indications into the design and fabrication of the cost-effective and environmentally benign catalysts with excellent adsorption and catalytic oxidation performances for HCHO removal at room temperature.

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