High-energy inositol pyrophosphates, such as IP 7 (diphosphoinositol pentakisphosphate), can directly donate a β-phosphate to a prephosphorylated serine residue generating pyrophosphorylated proteins. Here, we show that the β subunit of AP-3, a clathrin-associated protein complex required for HIV-1 release, is a target of IP 7 -mediated pyrophosphorylation. We have identified Kif3A, a motor protein of the kinesin superfamily, as an AP3B1-binding partner and demonstrate that Kif3A, like the AP-3 complex, is involved in an intracellular process required for HIV-1 Gag release. Importantly, IP 7 -mediated pyrophosphorylation of AP3B1 modulates the interaction with Kif3A and, as a consequence, affects the release of HIV-1 virus-like particles. This study identifies a cellular process that is regulated by IP 7 -mediated pyrophosphorylation.
Whole genome sequencing revealed that the complexity of higher organisms is not only linked to the number of genes but also to the evolution of a wide range of additional regulatory features such as post‐translational modification of proteins (PTMs). Almost all proteins can be modulated in this way, adding a level of complexity much greater than each gene product. PTMs can be very complex in nature and occur enzymatically and non‐enzymatically.
We identified and characterized a new PTM mediated by inorganic polyphosphate (polyP). This linear polymer of orthophosphate linked by ‘high‐energy’ phosphoanhydride bonds, analogous to those found in ATP, is ubiquitous in nature. We named this modification “polyphosphorylation” as it represents the covalent attachment of polyP to target proteins. We found that Nuclear signal recognition 1 (Nsr1) and its interacting partner, topoisomerase 1 (Top1) are polyphosphorylated at lysine residues within a conserved N‐terminal P oly A cidic serine ( S ) and lysine ( K ) rich (PASK) cluster. Polyphosphorylation negatively regulates Nsr1/Top1 interaction and impairs Top1 enzymatic activity of relaxing super coiled DNA. We demonstrate that modulation of cellular levels of polyP regulates Top1 activity by modifying its polyphosphorylation status. We propose that polyphosphorylation represents a new regulatory mechanism of acidic proteins known to be enriched in the nuclei of both yeast and mammalian cells. Polyphosphorylation of these proteins may add an additional layer of regulation to nuclear signaling, in particular to one of the most energy‐consuming and tightly regulated process in eukaryotic cells, ribosomal RNA biogenesis, where Nsr1 and Top1 play roles.
Inorganic polyphosphate (polyP) is a ubiquitous polymer that controls fundamental processes. To overcome the absence of a genetically tractable mammalian model, we developed an inducible mammalian cell line expressing Escherichia coli polyphosphate kinase 1 (EcPPK1). Inducing EcPPK1 expression prompted polyP synthesis, enabling validation of polyP analytical methods. Virtually all newly synthesized polyP accumulates within the nucleus, mainly in the nucleolus. The channeled polyP within the nucleolus results in the redistribution of its markers, leading to altered rRNA processing. Ultrastructural analysis reveals electron-dense polyP structures associated with a hyper-condensed nucleolus resulting from an exacerbation of the liquid-liquid phase separation (LLPS) phenomena controlling this membraneless organelle. The selective accumulation of polyP in the nucleoli could be interpreted as an amplification of polyP channeling to where its physiological function takes place. Indeed, quantitative analysis of several mammalian cell lines confirms that endogenous polyP accumulates within the nucleolus.
Plant disease resistance ( R ) genes trigger innate immune responses upon pathogen attack. RAR1 is an early convergence point in a signaling pathway engaged by multiple R genes. Here, we show that RAR1 interacts with plant orthologs of the yeast protein SGT1, an essential regulator in the cell cycle. Silencing the barley gene Sgt1 reveals its role in R gene–triggered, Rar1 -dependent disease resistance. SGT1 associates with SKP1 and CUL1, subunits of the SCF (Skp1-Cullin–F-box) ubiquitin ligase complex. Furthermore, the RAR1-SGT1 complex also interacts with two COP9 signalosome components. The interactions among RAR1, SGT1, SCF, and signalosome subunits indicate a link between disease resistance and ubiquitination.
Synthesis and physico-chemical properties of six 3-(4-bromophenacyl)-5-arylidene-thiazolidine-2,4-diones and eight 3-(4-chlorobenzyl)-5-arylidene-4-thio-imidazolidine-2-ones are described. These products were synthesized by an aldolisation-crotonisation reaction from aromatic aldehydes and 3-substituted thiazolidine-2,4-diones or 4-thio-imidazolidine-2-ones. Hypoglycemic and peripheral antinociceptive activities were investigated for these compounds.
'%3e%3cpath fill='%23012169' d='M0 0v30h60V0z'/%3e%3cpath stroke='%23fff' stroke-width='6' d='m0 0 60 30m0-30L0 30'/%3e%3cpath stroke='%23C8102E' stroke-width='4' d='m0 0 60 30m0-30L0 30' clip-path='url(%23b)'/%3e%3cpath stroke='%23fff' stroke-width='10' d='M30 0v30M0 15h60'/%3e%3cpath stroke='%23C8102E' stroke-width='6' d='M30 0v30M0 15h60'/%3e%3c/g%3e%3c/svg%3e)
