SUMO-2 promotes mRNA translation by enhancing interaction between eIF4E and eIF4G

Application of SUMO fusion technology for the enhancement of stability and activity of lysophospholipase from Pyrococcus abyssi

Heterologous production of proteins in Escherichia coli has raised several challenges including soluble production of target proteins, high levels of expression and purification. Fusion tags can serve as the important tools to overcome these challenges. SUMO (small ubiquitin-related modifier) is one of these tags whose fusion to native protein sequence can enhance its solubility and stability. In current research, a simple, efficient and cost-effective method is being discussed for the construction of pET28a-SUMO vector. In order to improve the stability and activity of lysophospholipase from Pyrococcus abyssi (Pa-LPL), a 6xHis-SUMO tag was fused to N-terminal of Pa-LPL by using pET28a-SUMO vector. Recombinant SUMO-fused enzyme (6 H-S-PaLPL) works optimally at 35 °C and pH 6.5 with remarkable thermostability at 35-95 °C. Thermo-inactivation kinetics of 6 H-S-PaLPL were also studied at 35-95 °C with first order rate constant (kIN) of 5.58 × 10- 2 h-1 and half-life of 12 ± 0 h at 95 °C. Km and Vmax for the hydrolysis of 4-nitrophenyl butyrate were calculated to be 2 ± 0.015 mM and 3882 ± 22.368 U/mg, respectively. 2.4-fold increase in Vmax of Pa-LPL was observed after fusion of 6xHis-SUMO tag to its N-terminal. It is the first report on the utilization of SUMO fusion tag to enhance the overall stability and activity of Pa-LPL. Fusion of 6xHis-SUMO tag not only aided in the purification process but also played a crucial role in increasing the thermostability and activity of the enzyme. SUMO-fused enzyme, thus generated, can serve as an important candidate for degumming of vegetable oils at industrial scale.

Uncover New Reactivity of Genetically Encoded Alkyl Bromide Non-Canonical Amino Acids

Genetically encoded non-canonical amino acids (ncAAs) with electrophilic moieties are excellent tools to investigate protein-protein interactions (PPIs) both in vitro and in vivo. These ncAAs, including a series of alkyl bromide-based ncAAs, mainly target cysteine residues to form protein-protein cross-links. Although some reactivities towards lysine and tyrosine residues have been reported, a comprehensive understanding of their reactivity towards a broad range of nucleophilic amino acids is lacking. Here we used a recently developed OpenUaa search engine to perform an in-depth analysis of mass spec data generated for Thioredoxin and its direct binding proteins cross-linked with an alkyl bromide-based ncAA, BprY. The analysis showed that, besides cysteine residues, BprY also targeted a broad range of nucleophilic amino acids. We validated this broad reactivity of BprY with Affibody/Z protein complex. We then successfully applied BprY to map a binding interface between SUMO2 and SUMO-interacting motifs (SIMs). BprY was further applied to probe SUMO2 interaction partners. We identified 264 SUMO2 binders, including several validated SUMO2 binders and many new binders. Our data demonstrated that BprY can be effectively used to probe protein-protein interaction interfaces even without cysteine residues, which will greatly expand the power of BprY in studying PPIs.

PIASγ controls stability and facilitates SUMO-2 conjugation to CoREST family of transcriptional co-repressors

CoREST family of transcriptional co-repressors regulates gene expression and cell fate determination during development. CoREST co-repressors recruit with different affinity the histone demethylase LSD1 (KDM1A) and the deacetylases HDAC1/2 to repress with variable strength the expression of target genes. CoREST protein levels are differentially regulated during cell fate determination and in mature tissues. However, regulatory mechanisms of CoREST co-repressors at the protein level have not been studied. Here, we report that CoREST (CoREST1, RCOR1) and its homologs CoREST2 (RCOR2) and CoREST3 (RCOR3) interact with PIASγ (protein inhibitor of activated STAT), a SUMO (small ubiquitin-like modifier)-E3-ligase. PIASγ increases the stability of CoREST proteins and facilitates their SUMOylation by SUMO-2. Interestingly, the SUMO-conjugating enzyme, Ubc9 also facilitates the SUMOylation of CoREST proteins. However, it does not change their protein levels. Specificity was shown using the null enzymatic form of PIASγ (PIASγ-C342A) and the SUMO protease SENP-1, which reversed SUMOylation and the increment of CoREST protein levels induced by PIASγ. The major SUMO acceptor lysines are different and are localized in nonconserved sequences among CoREST proteins. SUMOylation-deficient CoREST1 and CoREST3 mutants maintain a similar interaction profile with LSD1 and HDAC1/2, and consequently maintain similar repressor capacity compared with wild-type counterparts. In conclusion, CoREST co-repressors form protein complexes with PIASγ, which acts both as SUMO E3-ligase and as a protein stabilizer for CoREST proteins. This novel regulation of CoREST by PIASγ interaction and SUMOylation may serve to control cell fate determination during development.

eIF4E Resistance: Natural Variation Should Guide Gene Editing

eIF4E translation initiation factors have emerged as major susceptibility factors for RNA viruses. Natural eIF4E-based resistance alleles are found in many species and are mostly variants that maintain the translation function of the protein. eIF4E genes represent major targets for engineering viral resistance, and gene-editing technologies can be used to make up for the lack of natural resistance alleles in some crops, often by knocking out eIF4E susceptibility factors. However, we report here how redundancy among eIF4E genes can restrict the efficient use of knockout alleles in breeding. We therefore discuss how gene-editing technologies can be used to design de novo functional alleles, using knowledge about the natural evolution of eIF4E genes in different species, to drive resistance to viruses without affecting plant physiology.

A ribosome-related signature in peripheral blood CLL B cells is linked to reduced survival following treatment

We have used polysome profiling coupled to microarray analysis to examine the translatome of a panel of peripheral blood (PB) B cells isolated from 34 chronic lymphocytic leukaemia (CLL) patients. We have identified a ‘ribosome-related' signature in CLL patients with mRNAs encoding for ribosomal proteins and factors that modify ribosomal RNA, e.g. DKC1 (which encodes dyskerin, a pseudouridine synthase), showing reduced polysomal association and decreased expression of the corresponding proteins. Our data suggest a general impact of dyskerin dysregulation on the translational apparatus in CLL and importantly patients with low dyskerin levels have a significantly shorter period of overall survival following treatment. Thus, translational dysregulation of dyskerin could constitute a mechanism by which the CLL PB B cells acquire an aggressive phenotype and thus have a major role in oncogenesis.

SUMOylation of Rb enhances its binding with CDK2 and phosphorylation at early G1 phase

Retinoblastoma protein (Rb) is a prototypical tumor suppressor that is vital to the negative regulation of the cell cycle and tumor progression. Hypo-phosphorylated Rb is associated with G0/G1 arrest by suppressing E2F transcription factor activity, whereas Rb hyper-phosphorylation allows E2F release and cell cycle progression from G0/G1 to S phase. However, the factors that regulate cyclin-dependent protein kinase (CDK)-dependent hyper-phosphorylation of Rb during the cell cycle remain obscure. In this study, we show that throughout the cell cycle, Rb is specifically small ubiquitin-like modifier (SUMO)ylated at early G1 phase. SUMOylation of Rb stimulates its phosphorylation level by recruiting a SUMO-interaction motif (SIM)-containing kinase CDK2, leading to Rb hyper-phosphorylation and E2F-1 release. In contrast, a SUMO-deficient Rb mutant results in reduced SUMOylation and phosphorylation, weakened CDK2 binding, and attenuated E2F-1 sequestration. Furthermore, we reveal that Rb SUMOylation is required for cell proliferation. Therefore, our study describes a novel mechanism that regulates Rb phosphorylation during cell cycle progression.